Full frame will never be very inexpensive. Semiconductors are priced by area. Unlike processors, going to a smaller process node doesn't make the size (area) of the full-frame sensor smaller and therefore doesn't decrease price. Thom Hogan has a recent article that mentions that phenomenon:
http://www.dslrbodies.com/newsviews/tough-camera-questions.html As for APS-C versus MFT. I don't think there is a lot to differentiate them, but one important thing to remember is MFT sits between Canon and Nikon in the smaller-sensor image quality heirarchy. Put another way: the latest MFT sensors have higher quality than the latest Canon APS-C sensors. The latest Nikon (sony) sensors are better than the latest MFT sensors. Truthfully, there is little to differentiate MFT from APS-C from an IQ point of view. There is a difference, but it is small.
Lens size is the most substantial difference between current APS-C cameras and mirrorless MFT cameras. The ability to have a short flange distance AND a smaller imaging circle makes MFT lenses much smaller than the APS-C lenses on cameras with mirrors. Some of the mirrorless APS-C cameras (NEX and Fuju) have closed the gap, but there is a limited selection of smaller APS-C lenses that are dedicated to these bodies.
Smaller bodies of the MFT format is great, but smaller lenses is even better. There are two advantages to the smaller lenses. The first is obviously they are smaller and you can carry more lenses for the same weight. The second advantage is that because of the smaller imaging circle, you don't need to manufacture as large a chunk of excellent glass to make an excellent lens. This meas less scrap material and better quality in manufacturing.
I don't think APS-C or MFT are going away. I think mirrored APS-C and MFT are probably going to become a niche product....though this may take many more years. The only application for APS-C with a mirror is wildlife and sports photography where you like the crop factor for its "increased reach" effect. This advantage may be eliminated when full frame pixel densities exceed those on APS-C, but even with the D800 that hasn't happened yet. The system that will exist between the phone cameras and the full-frame DSLRs will be smaller sensor APS-C and MFT cameras, some with interchangeable lenses, but all with EVFs. Price will come down in this category as they have with DSLRs.
As for the financial solvency of the camera industry and most notably everyone except Canon and Nikon: Large multinational companies like Sony, Panasonic, and Olympus don't stay in businesses only for direct profit. There are two other things at issue: they can't ignore what they see as a lucrative market that they might be able to capitalize on in the future, and they see their investment in the business as having benefits to other parts of their company. For Olympus this is trickle-down technology from consumer cameras to medical imaging (their real profit center). For Sony and Panasonic this probably involves their interest in maintaining hegemony in their very profitiable video camera markets with the coming merge between the still and video camera markets. Of course, there may be other reasons to stay in less-than-profitable markets including things like public relations and marketing, maintaining their corporate identity, or a true belief in the vision of their leadership. Finally, remember that Canon and Nikon's camera businesses haven't exactly been growing by leaps and bounds either. I believe that Nikon lost money in the last quarter and has been up and down lately. Canon, of course is highly diversified (like sony or panasonic) into printers, copiers as well as their cameras.
The whole industry is contracting. It will be painful. Some companies will leave the market, but if this is your business, you fight to stay in it. Olympus and Pentax will probably struggle, but this is what they do and they remain pretty good at it, so don't count them out.
