99 years devalues as time goes by, when your lease is left 70, 60 or 50 years, you will already start to see a visible lower price. Tis true that the house will likely last longer than one's lifetime. Tis also a fact, your next generation will confirm have to buy their own house.
FH though, can still be taken back if the government requisitions the land, for whatever purpose they can contrive. They can pay you market value for land, market value is subjective though, market value is not fair value as my relatives found out. Along with other affected parties, they fought with the government all the way to high court , hired a QC, the surveyor can admit it's not fair value, but the court still rule in the government's favour, citing robin hood law or something like that. They were only getting like half of the open market value, this will likely be the case, unless your neighbour is an MP, then you will get a generous payout.
That said, my recommendation is still to go for FH even at a slight premium, reason being the amount of FH land is limited. Most of it is already built up. So you will see mostly 99 years developments in future. Don't forget FH can enbloc, 99 years no such thing.