This trend will continue. At some point, though, we should see a leveling off of SL losses while OpenSim will continue.
I'm basing this on my own subjective understanding of human nature. People will suffer only so much crappy treatment from a company before they will leave to seek another, hopefully better, one.
The people who are in the Metaverse, whether OpenSim, AuroraSim, SL or any other, similar, virtual world, fall in love with them. They will not be willing to give them up. So, they will teach themselves how to use OpenSim and will be pleasantly surprised with how easy and affordable it is. And they will tell their friends. That will be the "grass roots" of the growth of OpenSim.
Yet, there are those who will continue to be die hard fans of SL and will remain. There will always be those who will give it a try, with many leaving but some few remaining. This will eventually strike a balance between those who leave and those who will give it a chance.
I have no idea of how long that will take, but I would not be surprised if it was along the time-line of the Gartner Hype Cycle, which Maria wrote about some time ago.