Like u/DukeOfAlexandria said, once the plastic is brittle enough to break like that, you most likely have to replace it. Even if you could cut that nipple out, and epoxy it back on, it’s likely to just snap or crumble when you try and get the hose back on. Odds are the whole nipple is just going to crumble to dust trying to get it out of the hose…
If the radiator is degraded, hoses are likely bad/need to be replaced. If there’s a plastic thermostat housing, etc., assuming those pieces are degraded as well. If you have to replace the thermostat, assume the housing is bad so you have the parts for it.
Like u/DukeOfAlexandria said, once the plastic is brittle enough to break like that, you most likely have to replace it. Even if you could cut that nipple out, and epoxy it back on, it’s likely to just snap or crumble when you try and get the hose back on. Odds are the whole nipple is just going to crumble to dust trying to get it out of the hose…
If the radiator is degraded, hoses are likely bad/need to be replaced. If there’s a plastic thermostat housing, etc., assuming those pieces are degraded as well. If you have to replace the thermostat, assume the housing is bad so you have the parts for it.