There are several players in what I like to call the "Thousand Hour" club, I'm getting close with about 900 now. Some have gotten a bit burnt out like you said due to the wipes over the last year or so, and others keep trucking along. Some like me take breaks in between server wipes, and/or jump ship to other servers for a fresh start.
If you look at Steam Charts,
http://steamcharts.com/app/290080#6myou'll see that for the since July, the population of Peak Online players has stayed pretty consistent at just over 1000 players. When the Early Access was more new, November of 2014 to May 2015, we often saw numbers more in the 2-3k range. This is not abnormal at all. Gamers get tired of wipes, get interested in other titles, or just feel like moving on.
My guess for the launch of the MMO, will be roughly 5-7k players who have bought the LiF:YO game and will get their first character free, and another 5-10k new buyers (maybe more) depending on the hype generated as well as advertising. Once the early rush is over, it will all depend on how successful the launch is conducted. If done well, the playerbase will likely grow for the next 3-6 months.
If it's rocky however, it will likely stagnate and likely drop off down to the 1-3k range where only the diehards and fanbois are left, until they get the game steady. Then it all depends on their recovery methods. Some games survive a bad launch, others stifle and die out. Thankfully more independents recover from a bad launch than do so the big labels with a publisher backing them.
As for release, for LiF:YO they are saying November 2015 for final polishing before release, so I'd expect the full release of the game to be November/December of this year (2015). MMO testing will start shortly after that, I've heard March 2016 as an estimated date for closed Alpha testers. The recent AMA with Bobik:
ama-with-bobik-on-twitch-t15166/page10/MMO testing is expected March 2016, no date for the official MMO yet. Alpha tester will have early access to the MMO test.