I suspect that when our generation of Bitcoin holders dies, a lot of us will not have left information for our heirs to access our wallets.
Why not? It's not like you can take it with you.
You may not share your wallet information with your heir if:
-You die in an unexpected accident such as a car crash and did not share your wallet information or write a will because you thought you were going to live longer and that there would be time for it later.
-You hold a low amount of BTC and believe that bothering to share your wallet information would be a waste of time for such an insignificant amount.
-You don’t care what happens after you die.
-You don’t have anyone you want to leave your belongings to.
and is there a way to stop it?
Not without a hard fork and agreement from the vast majority of all participants (miners, nodes, merchants, users, exchanges, speculators, etc). Getting that sort of agreement on changing the very nature of bitcoin, a nature that most of them desire in the first place, is effectively impossible. It isn't going to happen. Why would you want to stop it anyhow? This is one of the great features of bitcoin.
In the long run, if 50% of Bitcoin’s total supply becomes inactive will people still want to use it?
Absolutely! Why wouldn't you? You get to have the exact same number of satoshis, but they are worth twice as much money. Isn't this a good thing?
It is a good thing if you look at it in terms of price. If you hold Bitcoins then it is fantastic because what you hold gains value. However, looking at it from another angle, the market cap becomes misleading as more inactive coins exist. I think that Bitcoins that can never again be in circulation should not be used in the calculation market cap. It would be like measuring today’s Plutonium market cap and also including the amount that has been lost to radioactive decay. I guess though, that inactive Bitcoins (and other cryptocurrencies) would be more of a problem for ranking sites like coinmarketcap than the actual holders. I personally can’t think of any direct negative effect inactive coins would have on the actual holders.