Gas water boiler: replace or no?

PadKraPow

I have a small house in Alaska with NG. The boiler is original to the build (1985), and is a HydroTherm. It's ticking away and hasn't given me any issues.
However, I had some leaky pipes and the random plumber I called said absolutely to replace the boiler before snow flies. End of its lifespan, etc. I figured I may as well condense from boiler + water heater to a combi.
So later I called another guy who was highly recommended. He said yes, combi, he loves Lochinvar, and gave me a quote. Now I can't reach him, so I called a couple other people.
One says he only does Navien but he hasn't yet had a chance to come look at my boiler.
Another came to look and said that he absolutely wouldn't replace it, as combi models are being discontinued too often and parts are seldom stocked in state (and in winter in Alaska, that is a concern) and, moreover, the standard workhorse HydroTherm is gonna keep going for ages and parts are easy to get. He recommended a thorough servicing and maybe a new water heater, but said nix the replacement.

So now I have one plumber saying ditch it FAST, and another saying no, it's all fine.
What the heck now? I definitely don't want it shitting the bed in January, but I also don't want to drop $ if it's really not needed. OTOH I have the money now, so if it's a case of "you might as well do it now," then I'd as leif do it now.

Do HydroTherms really just keep going for 50 years? I'd appreciate input.