Will they? Isn't it the same case with email? I used my University email when I was a student. I have a different company email for different jobs? Those that needed to communicate with me because of the job, I would give them my company email. When my work at company X ended, no one expected me to still message me at raphael@x.

The same with addresses from "email providers". They change less often, but it is still possible. My first account was probably at yahoo, but when gmail came up, I migrated, started to tell people my new address and auto forwarded any message that went to the old email.

"Well", that may be a lot of work to some people. To which the answer is "the only way to have absolute stability regarding your identity is if you own it". You can buy a domain a use a managed email service, you can have a domain and have a managed activitypub service provider.

I really don't get people's confusion over federation. It's just like email.