How is it easy to trade Thornton? He has a pretty large salary, and doesn't offer that much ability wise.
Also I find it odd that you think Phoenix would trade Bledsoe to play a relatively unproven Euro player. I know Bledsoe and Phoenix have had their issues, but Phoenix has the opportunity to field one of the strongest backcourt rotations. Not sure they'd just give that up.
I don't think Z. Dragic would be meant to "replace" Bledsoe, just that they did sign Isaiah Thomas and still have G. Dragic for at least a year so they wouldn't have a hole at the position if they lose Bledsoe. The thing is, he wants a max deal and it's clear from the stalemate Phoenix is not eager to give it to him. If they can get something for him and save that money for a potential G. Dragic re-sign next year, that might not be a bad way to go. Let's remember that Bledsoe is coming off a serious injury and hasn't shown great durability during his career.
Even though Thornton's deal is large, it only runs for one more year. I think the Celtics could make him a reserve, have him go home like Keith Bogans, or find a team under the cap to take his salary for a 2nd rounder or something. They could even deal it for another expiring of the same amount or a little less. If they want to get rid of him, I think they could without costing them a lot. Not that I'm necessarily advocating that, I was just making the point that they shouldn't be avoiding moves at the SG position just because they happen to have a bunch of mediocre players at the position right now, besides Bradley of course (who's not exactly a star either).