What happens when?….

Need to preface by saying I’m a maxi, invested, promoting, and true believer. This is not a criticism, simply a question…. If layer 2 solutions are the answer to the scaling problem, and I believe they are, then what happens in about 100 years when all the coins are mined and the only incentive to mine will be the tx fees? But all the transactions have moved to layer 2? So where is the incentive to mine? And what happens to the security of the network when so few people are left mining? I’ve just finished “The Bitcoin Standard” which addresses a lot of my questions, but not this one.