Roger Ver will be as relevant as the number of coins he has, and if he chooses to dump them, then more power to him. I think quite a few people will be just happy to jump at this opportunity and buy his coins when the price flash crashes after he sells his stash of bitcoins (though I sincerely doubt whether he is actually going to sell anything).
Roger Ver has been offered to trade his Bitcoins for BU coins at the time a hard fork has been initiated, but of course, he never responded - which is more or less the same as simply saying no. In that regard, it's safe to assume that he will never sell his Bitcoins. Mainly because of the fact that his wealth (according to various articles, it is in the range of a few hundred thousand
BTC) is exactly that what gives him his power.
Again, Jihan Wu will likely also lose some of his influence between miners as well as miners themselves will be less relevant with the introduction of first SegWit and then Lightning Network
Correct, but as long as he accounts for a large percentage of the total network, he will remain an important factor in the whole picture. Him and Ver combined makes a very powerful duo. In that regard, even with SW and LN activated, they will remain forming a massive obstable.