Ten years is a very long time in tech. I wouldn't be confident that the Airtag protocol will be functioning in 2035, and there are already rumors of a new Airtag and possibly a newer protocol coming up.
I'm sure Apple will innovate and come up with something newer/better/etc at some point. But it's unlikely the gen1 devices will go away anytime soon. Even if the real life is only... 5 years, that still saves a number of battery changes for devices that maybe you don't want to deal with regularly.
And with the fact that Apple had enough demand to increase the limit from 16 to 32 per account ( https://9to5mac.com/2024/01/12/airtag-limit/ ). Clearly people have bought into the ecosystem in a big way. 30 Airtags * $25 each is $750. I don't think they'll decommission the gen1 system anytime soon with that much investment. Plus Apple is surprisingly good at supporting their hardware for a reasonable amount of time. The iPhone XR from 2018 is still supported by iOS 18.