I think I discovered the problem and fixed it.

I received an email this morning from SE telling me to reset my password (specifically, "Based upon recent suspicious activity, we have identified that your account may potentially be at risk. For your protection, we have temporarily suspended login access to this account.") I thought it was a phishing scam so I ignored it. When I went to mog station to find a client to download I got an error message related to that e-mail. Followed the instructions, reset my password, and I could log into the launcher again.

My bet is there's some error message I'm supposed to get from the launcher that didn't work, thus crashing the launcher.