I've read on another site (411mania) that Nexus are going to hold all the titles (excluding Divas title, unless the NXT 3 girls join, which would be EPIC! Naomi and Aksana, with AJ and Kaitlyn on SD) like Evolution did when they were about.
So I expect that The Nexus retain the titles and Barrett becomes the WWE Champion, and then eventually, Daniel Bryan drops the title to David Otunga.
The Nexus will continue up until the draft after Mania. Then they will be split up and put on different brands, but could possibly team them all up as tag teams (Harris and McGuilicutty; Slater and Gabriel) and build the tag divison around them, with Barrett and Otunga as the 'breakout' singles stars.