You can expect modern stainless frets to last 2-3 times as long as standard nickel-silver frets. They are harder and more durable than nickel-silver, but they aren't indestructible. When stainless fretwire first started appearing on the market, back in the 1990's, some of that was much harder material, and quite difficult to work with. The stainless wire available today is a little softer; a good compromise between durability and ease of installation. I suspect that within a few years, stainless fretwire will be standard on almost all guitars and basses.
I switched over to using stainless several years ago, on all of the basses I build and restore. I use the Jescar wire. After a bit of a learning curve, I've found that the stainless fretwire is actually less labor to install than nickel-silver. These days, I'll only use nickel-silver on restorations where the owner wants to be really picky about authenticity.