Good post ! This is one of those problems that it's impossible to plan for; sometimes a seal will last forever, other times they'll just randomly fail. It could have been worse, the other main place you can get coolant leaking into the engine is if the cylinder head gasket goes, which (depending on the engine) can be a lot of work to replace.
But you were right not to use the bike too much once you identified the problem. If the oil is contaminated with coolant, it won't provide lubrication for the engine bearings, and if you have to replace the big end, small end, and con-rod bearings, that is a job where it is probably just cheaper to put a second-hand engine in !