It's very unlikely for a solar company, whether an installer or manufacturer, to last 25 or 30 years. I worked in equipment sales and our suppliers would routinely go out of business or be on the verge of bankruptcy. We'd advertise warranty insurance and reinsurance because it was assumed that the company wouldn't be there that long from now.

If you just have modules (the panels themselves) on the roof that long you'd probably be okay, but if you have microinverters or power optimizers under them, those power electronics have a finite lifespan and will eventually die. Or if a single module wired in series goes bad, you'd still have roof work to do.

It's not just install and forget. It's install and pray you don't have to do too much work too soon...

(Edit: Ideally, these systems would pay for themselves in a few years. As long as that happens before they die, you'd still come out ahead. But that's not always the case. My last company got sued because the stuff we made kept failing -- it was in the news, so no company secrets there. One of our major installers also went bankrupt. Depending on who you ask, our equipment may or may not have been at fault.)