Without a doubt, the most popular and probably most effective way of having Daniel Bryan return from injury would be as a surprise entrant in the 2015 Royal Rumble. The same thing has worked twice before off the top of my head, and that being the returns from injury of John Cena in 2008 and Edge in 2010. On each occasion, they have won their respective Rumble matches entering at #30 (Cena) and #29 (Edge) and gone on to main event that year's Wrestlemania. There would be a great feeling of justice being served if this was to happen to DBry, as many believe that he should have won 2014 Royal Rumble match, and despite still winning the big one just months later at Wrestlemania, it is thought that Batista and Rey Mysterio (who still gets heat for being the last entrant instead of DBry) took a special moment away, and that Bryan should have won the Rumble, and then went on to main event Mania. That's been and gone though, and we're looking to the future, should WWE manage to keep Bryan's return under wraps, the roar that would fill the arena when Flight of the Valkyries hits at entrant #30 would be unparalleled, and even more so when he claims the win, throwing himself straight back into the championship picture. This would be ideal for Bryan, as it allows him that extra time in order to fully recover.
However, should he be cleared earlier than expected, it's perfectly viable that Bryan makes a surprise return at an earlier PPV. After Brock has defended the title, the closing scenes could be of Bryan standing on the stage, making it clear that he's back, and wants what rightfully belongs to him. It could also be used as the first time that Lesnar sees someone as a proper threat to his title reign. After making short work of John Cena again at Night of Champions, and then another likely contender such as Roman Reigns, the return of Bryan may startle him a bit, and losing to him would make it even worse for The Beast Incarnate and his advocate, Paul Heyman. Of course, a brutal match up in which Bryan shows the desire and heart that won him the WWE World Heavyweight Championship, and the hearts of almost every wrestling fan in the world in the first place, would likely open the door for Seth Rollins to finally cash in his Money in the Bank briefcase. After the match with Lesnar, it would surely be an open goal for Rollins to come down to the ring and simply take the title for himself, potentially setting up a triple threat between himself, Bryan and Lesnar at one point. That last part is wishful thinking, but it would personally be my favorite option as I've expected Bryan and Rollins to fight over gold in WWE in the future, but it's very possible it'll happen sooner rather than later.
Finally, another thought that has crossed my mind recently that if, like the previous scenario, he is cleared much earlier, he may be a surprise team member in the traditional Survivor Series tag team match. The prestige and relevancy has somewhat died from the match in recent times, with last year's being the best in a while, seeing Roman Reigns single-handedly win the match for his team. With this one, they could choose to go down an anti-Authority storyline, in which they have Triple H, Randy Orton, Seth Rollins, Kane and the returning Batista up against a selection of superstars done wrong by the Authority. An obvious leader of that team would be Dean Ambrose, who certainly has enough cause. He would assemble a team of other superstars who have been mistreated in the past few weeks, mostly midcarders such as Cesaro or Jack Swagger being included, as well as a big guy such as Big Show or Mark Henry. However, the Monday before Survivor Series, the Authority would beat down one of the bigger men, leaving him unable to compete, and a place on Ambrose's team open for someone. Come the night, it looks as though it'll be 5 on 4, but Ambrose reveals he found someone more than willing to come down and lend a hand, cue a thunderous ovation as Bryan returns, reminiscent of his joining of team WWE to take on the Nexus at the start of his WWE career. It would be symbolic of his career coming full circle, and being ready to start from scratch all over again to get back to the top, starting by helping take down the very people who made his life hell the whole time he pursued and held the WWE World Heavyweight Championship.
Any one of those options would be incredible, but of course, he needs to recover first, and all we can do until then is hope that his injury heals up well and we get to see him back doing what he does better than anyone else on this planet...
Wrestle.