I give everyone 3 active activations. This means they can activate on up to 3 machines. If someone gave me money, I trust them to use it for themselves only. The license is per seat, so it should be a single user operating my software on these 3 machines. Are people abusing that? Certainly. I don’t care. If people are abusing the licensing, they wouldn’t pay for another license anyway and I don’t like to be a police to my users.
So, if their machine crashes, they can log into my website, deactivate the machine they no longer use and free up one activation.
The longer you sell your lifetime licenses, the more people you have who will ask you for the help in the future. They may be great users, but that will be drain on your resources.
I suggest to simply sunset the version you have now on the next significant rewrite and offer a separate SKU for the new version. Your old users still get to use the version they purchased forever, as well as install it when it crashes. They just don’t get to ask you things to fix or help in 2035, as is happening to me. Business changes. The most expensive version I used to have back then is now 10x less money than the current most expensive version - and there a no more lifetime licenses.
Also, I am introducing maintenance subscription (30% of the list price per year). If they cancel the maintenance, they keep the version they originally bought but lose technical support and upgrades when the maintenance expires.
Hope this helps.