I know this, Treyarch will release a non-MW game next year and MW4 will land in 2013.Professor James said:There can be other call of duty games besides the modern warfare series. And it would be kind of hard to another MW4 becauseThey killed Makarov and Soap. There isn't really much loose ends to go after now.
As for the plot, that's irrelevant, there were no loose ends at all at the end of Modern Warfare. You won, NATO and Russia were (covertly at least) in full military co-operation, the bad guy(s) had all been killed and the 'good' Russians had arrived in force to rescue you and take out whatever remained of Zakaev's supporters, having been given the excuse to go to full scale war against them since they were arranging nuclear attacks on other countries.
Yet MW2 still happened with a healthy dose of makeitaswegoalong-ium to create a plot. Price is still alive so the money shot character is still there, no doubt Makarov has some lackey we've never heard of yet who will take over and we'll find out that it was the Chinese all along (or something).
Modern Warfare is too valuable a franchise to end, it'll be back in two year's time.