1) Has the "Mini Dump" crashing problem finally been resolved?
Yes, for the most part. About a month ago, a major cause of desyncs and minidumps was fixed.
2) Is there an active online multiplayer community?
Very sadly, no. People still play the game online, but you can really only find players during North American prime times and it still takes patience to find a game. Shortly after Diplomacy was released in early February, the online player counts dropped precipitously, perhaps because the community was divided, making it harder to find games. If you travel 5 months back in time, you would have seen multiple 5v5 games played every night. Here's an example of what I mean by low player counts. Let's look at the online player counts for April 12, 9:40 pm U.S. EST on a Monday night (prime gaming time):
Regular/Entrenchment server: 36 players online.
Diplomacy server: 42 players online.
That makes 78 players total online, but they are split up. Now, 5 months ago at this time, the number might have been 110 people online on one server (Regular/Entrenchment). (The people on the Regular/Entrenchment server cannot see the people on the Diplomacy server and vice-versa.) With 110 people on one server it wasn't too hard to find games but did require a little patience sometimes.
It's too bad that you gave up on Sins so early. It has been improved tremendously since then, especially with the Entrenchment expansion. Back when you played, only 20% of the players could host, etc. Since then the hosting problems have been fixed and many people have enjoyed a great many Sins games, often without any minidumps.
I think you should give Sins another try. See if you can find games for regular Sins. You're probably near noob level at this point, and the good news is that there are many new players on Regular Sins. Most of the pros, at least the ones who are still playing, purchased Diplomacy (which requires Entrenchment). Of the three versions of the game, my guess is that Entrenchment is the least played now.
Note that you will need to download and install Impulse to be able to update your game so that you can play it online. Impulse became Sins's form of DRM.