The only thing that is dropped to 0 is the block subsidy, and will happen in 120 years. 51% attack has nothing to do with it, and will always be possible to accomplish (although, unlikely) as long as there's the Bitcoin network.
This is what I was wondering about, In past replies, some were stating miners will only earn through transaction fee commissions, and I think there was hardly any reply focusing on dropping the block reward in btc fractions.
If the case of bitcoin reaching above 120 years occus then bitcoin should have at least 20Trillion marketcap, which is a very good possibility and I think can be achieved.
you cannot change bitcoin rules with a 51% attack. you can only change transaction lists by going back and re-doing a block and subsequent blocks where the re-done block has diffeerent transactions
in 120 years where the only mining income is from transactions.. it then becomes less likely risk of "empty blocks" because having no transactions = no income
however.
if the only income is transactions.. and thus if the total fee's are not totalling a high enough amount to make it expensive to compete on the network. thus not expensive to then re-org.. then that cheap attack makes it easier to perform than now.
so in the next 120 years we really need to push that total fee's per block are substantial amount to not make it cheap to attack.
..
this does not mean make each user pay alot more. as that just makes people not use the network and not do transactions.. but instead increasing the transaction count so the total fee's increase without hurting the average fee per user