I would suggest that 1000 hours might be close to the half life of a component like this. 2000 hours is the equivalent of 100,000 miles at 50 mph and most automotive alternators should easily do that.
I'll also tell you I once had the belt go with no spares. No alternator and no water pump. Foolish of me. But the battery will run the engine for a long time if you are not starting and stopping and using the battery power for much else. Easily an hour or two.
Can't say on the V8's but on my 4 cylinder if you keep the rpm's low in the range, maybe 1500-2000 where you might not get on plane, the impeller pump in the outdrive will keep the engine cool enough to prevent any over heating.
This happened to me years ago and we basically took a leisurely idle ride back to the dock with me watching the temp gauge closely and feeling the exhaust manifold from time to time to make sure we were not overheating and cooking something. Everything was just fine.
So I think you should be able to get somewhere if your alternator goes and you have to remove the belt to keep it from self destructing something.
In the aftermath and repair I discovered a couple thing. The pulleys like to rust and the alternator on mine was getting a little noisy. My alternator was still looking like new with <75 hours but one of the bearings was already a bit noisy. It was a pain to get the thing apart but I just put new bearings in it for a few bucks and it has been fine since. I spent a lot of time also cleaning the rust from the pulleys because that is what ate up the belt.
The real source of the whole problem was not keeping it dry dry in storage over the winter. Some water in the bilge meant condensation particularly in the engine compartment on the cold steel that rusted the bare metal pulleys. Maybe the bearing was corrosion or maybe just a random failure, IDK.
I should add that some alternators have very durable windings good for many rebuilds. New bearings and regulators make them as good as new. Not sure about these overpriced 'marine' alternators which I think are just automotive ones painted Phantom Black
Alternator life expectancy.
