Why could you not finish? Even if you crashed you can sign back in and reenter. Now that does not mean all pugs will wait for you, but every group I have been with has waited 5 to 7 mins for someone that crashed to sign back in.
Crashes happen, can't prevent that with so many types of hardware, but when they happen just do everything you can possibly do to get back to the group ASAP. Normally when I am in a group, we will continue clearing trash, but will wait to find a replacement for 7 mins (although I have been in groups that would only wait 5 mins). I once had someone wait 10 mins for me at the end The Esseles when I crashed after the last conversation, but before clicking on the thing to end the mission when my power flickered off. They could have just clicked and left, but they waited on me.
He probably didn't say "wait for me" and just logged off without saying anything. I always wait for people who get this bug, but if they don't say "I'll be back" then I replace them.