Not concerned, it won't have any affect on the operation or principles of Bitcoin. Even if there is a sell off, it will have no long term impact on the price. It might provide a buying opportunity though.
Yep agreed with you on all points. Is there any way to know how much BTC is expected to be returned ?
I honestly don't think there is way to predict it accurately. Value is subjective. Bitcoin, just like any currency or store of value, only has the value that people place in it. I believe over time more people will come to place more value in Bitcoin, and since it is strictly scarce, the value of each satoshi should rise. By how much??? I honestly don't know. Maybe more people will come to value it as a store of value, and if so it could take some of the market share away from other stores of value like gold. As fiat currencies continue to be destroyed by their issuers,more people might begin to value as a hedge against inflation. I'm sure there other ways that people might find value in Bitcoin, but right now my wife has dinner on the table, and I place a higher value on that than I do on continuing this post
Edit: I think I misunderstood your question. You were not asking about expected return on investment, you were asking how much bitcoin will be returned to MtGox victims. I think it's about 170,000 bitcoins.