Not many smaller boats use keyed rudder shafts. It can be done, but it's a lot of extra cost in machining, and generally not worth it. Just friction fitting is typically enough.
I don't know your boat, but most rudders have a retaining collar that actually holds them in place. The tiller usually mounts above this. So no generally loosing the tile rout of the boat isn't a concern. NOT that it couldn't happen. The upside is if it was that easy to get out, you likely have a bad retaining collar that needs fixing anyway
If you don't have a retaining collar, then the bearing are likely to have enough friction to keep the rudder in the boat as well, so long as the rudder isn't under any stress at the time. And if it falls out... Well that's what snorkel gear is for. I can't tell you how many regattas have at least one person swimming for a dropped rudder.
There is a pretty good line drawing of how a rudder is attached at Marine Surveyor School