Bart Ehrman is right that the tomb where Jesus’ body was laid is probably lost. There is a very famous church in Jerusalem knows as the Church of the Holy Sepulcher, which is the supposed site of the empty tomb, but very few scholars will agree that this is even likely to be the actual tomb, never mind that it in fact the actual tomb. Is this a problem? No! The fact is that Jesus’ tomb was empty. Once it was found to be empty, it was not an important place to the early Christians. It was only about 300 years later, specifically because of Constantine’s mother Helena, that we have a record of anyone even thinking to “discover” the empty tomb. By then, there was no way to decide which of the empty tombs near Jerusalem was the correct one. For all we know, that tomb may have been used for others. There is no way to know. Besides, what could an empty tomb tell us, even if we were to find it? Essentially, it would be a place with no evidence. What would a location with no evidence do to change what we already know–which is that the tomb was empty? The reason we know it was empty is that the resurrection was proclaimed in Jerusalem, just a few weeks (seven to be exact) after the resurrection. Therefore, whether we think we know where the empty tomb is or whether we do not changes absolutely nothing. Ehrman says that this empty tomb was not found by his disciples. What he is talking about is those who looked for it 300 years later. Naturally, they could not locate it!!! What does this tell us? Nothing. But this is typical of Ehrman, who likes to create as much negative spin for Christians as possible. Ehrman is a good scholar but he has a very strong anti-Christian bias, and whatever he says should be looked at with this in mind.
The answer to your second question is a very strong no! The Exodus and desert wanderings are not a fable. Now, here is the fact that you should bear in mind (after which I will explain why I am confident the Exodus is not a myth). The fact is that we have no hard archaeological evidence, either for the Jews being in Egypt or for the Exodus and wandering in the wilderness itself. There is a very good reason for this. Think about this. What would be the potential archaeological evidence left behind by totally impoverished slaves in Egypt? Zero. There is no conceivable kind of archaeological evidence to be left behind by slaves living in slave quarters in ancient Egypt. The fact that we do not have such evidence is quite simply NOT evidence that they were not there. In ancient history, lack of evidence for something, especially something that we would not expect to find evidence from, is NOT evidence that the event did not happen. The same (or similar) can be said about the wandering in the wilderness. It is true that we have no hard evidence for the wandering in the desert, but what would be the conceivable evidence that one could find? A fireplace? Footprints? It is simply inconceivable that there would be archaeological evidence, either of the Jewish slaves in Egypt or of their travels through the desert. By the way, there is hard evidence of the conquest, including evidence of the destruction of Jericho and Hazor around 1400 BC, plus one of the Tel el Amarna tablets, which mentions the “Hapiru” conquering and attacking parts of Canaan around 1400 BC (see my article on history and archaeology at the web site).
Now, let me tell you why I nevertheless believe that the enslavement in Egypt and the escape and wandering are both true–that they are not fables or myths. First, there is the evidence of the conquest, mentioned above, which is strong indirect evidence of the Exodus (and therefore the captivity). Second of all there are the books of Exodus through Deuteronomy. They have every semblance of being accurate history. The entire Jewish Law is based on actual events which actual people actually living back then believed were true. The idea that Judaism could exist in its present form and that the first five books of the Bible, and indeed the Old Testament in general could exist if there was no person named Moses and there was no Exodus seems extremely unlikely. Then there is the evidence, in general, for the inspiration of the Old Testament. There are the dozens of messianic prophecies, including ones in Genesis and Deuteronomy, as well as many other prophecies in Deuteronomy (ch 28-29), all of which came true. Also, there are the myriad types, prefigures and foreshadows, especially in Leviticus, but also in the other books of the Pentateuch, all of which point very strongly toward the conclusion that these books are not only accurate history, but inspired documents. All of this evidence lends very strong credence to the historical reliability of Exodus through Deuteronomy. Is this absolutely proven by the data? I suppose there is room for doubt here, but my mind is entirely satisfied that these are actual events. Let me add that there is archaeological evidence which supports the historical reliability of Genesis as well. If Genesis is reliable history, then obviously, Exodus is as well. I will go ahead and attach the material on Archaeology and History to this e-mail to save you having to look it up.
I hope this helps.