Yes, a netsplit is almost always temporary. Of course, "temporary" can be anything from seconds to hours or more. Most last under 15 minutes.
You can get around a netsplit by just connecting to a server that is on the other "side" of the split.
5 servers are in a network and you connect to server #5. If a netsplit happens to #5, then everyone connected to #5 will no longer be able to see anyone connected to servers #1-4, and those on servers #1-4 won't see anyone on server #5. If you then go and connect to one of the #1-4 servers, you'd see everyone on those servers, but not on #5.
Depending on who is connected on each server and what channels they are in, you can very easily end up being the only person in a specific channel on server #5, so it will appear empty.
Of course, that's a basic example... netsplits can take out more than one server at a time, and you can even have multiple different splits, so that there are more than 2 sides to the split.