Fox has distribution rights to Episode IV for good, and for Episodes V and VI until 2020. Lucasfilm own the actual films themselves, and all decisions relating to their release lie with them. If Lucasfilm (or their new Disney masters) want to release the original original trilogy, they will do, and Fox will distribute them like they did the last few times. I very much doubt they could even refuse (not that they'd want to).
Fingers crossed original elements have been preserved well. Personally, a new Blu-ray release would only interest me if new scans/transfers were done of said elements, with proper colour correction and the original soundtracks. If you're going to release the unaltered Star Wars Trilogy, you get one shot and it better be done right. The fans have gone through way too much of Lucas' bulls*** to settle for something like the 2011 Blu-rays with the original footage, poorly sourced, reinserted (no doubt with a myriad of "mistakes" were proper corrections haven't been done).