If the engine has been running you can continue to do so for a questionable amount of hours. The leak will get larger and you should get it fixed at first opportunity but I wouldn't think another 50 hours would hurt much.

The cylinders won't all be firing equally and that can cause damage as that one will probably carbon up a bit more but diesels are a tough beast and the cylinder walls will take the abuse for a long time before needing sleeve replacement. If corroded the injector will need to be replaced but from the sounds if things, there is a compression seal that's gone and it may just be a matter of replacing that.

I would say no danger of complete engine failure; You've already seen the symptoms of hard starting and I suspect you have diesel odor permeating the cabin. That should be the worst of it beyond a possible sleeve and injector replacement.

Best of luck. I think you have time to search for a good mechanic and pricing