@Davy0
I know how hard it is for the hand to recover. From firsthand (no pun intended).
A simple broke (hand-bone), after the surgery (if needed) is in plaster for 6-8 week, then around the same time for "normal usage" rehab. After that, since you didn't used it in any pressuring activity you had to slowly work it up, what can take somewhere around another 3-6 month to get it back to around normal. 4,5-10 month. For an active athlete that IS a big pause, but not like they can't return after it. Or that (in this case) they has to completly shut down their work-out.
Of course, if its completly shattered thats a different story, then its possibile that you never regain 100% and the whol process can (and probably will) take more time, but for a boxer like Sendo, who mostly swings around his hands with 120% power, it still not that bad as it would been for others.
And after these, I still thought a forced retirement is possible. But then that "fistbump" happened, and thats why I'm saying it will be nothing career-breaking.
Morikawa wouldn't wrote that in, if, within 1 or 2 chapter Sendo has to retire due to hand injury. That would be bullshit, "getting the final blow while showing respect in a strange way..."
The thing is different if Sendo's hand "rebrokes" during a different fight but then again that could only happen after a new set-up, the recovery, and some chapters with others... Not in a short term.
And if anything, after why Ippo left boxing, it seems dumb for him to return to the ring cause one of his friend get not-too-seriously injured.
So my 2,5 prediction how Ippo could return right now is:
1. Sendo "rebreaks" his hand during a title match so he has to retire and Ippo wants to carry his will.
1,5 . The same but not a hand injury but a total complete life-threathening event, when Ippo makes an oath to revenge him.
3. Sendo wins vs Ricardo and Ippo want to fight with him again (I think its the least plausable, cause the scene, where Miyata says that Sendo already had his 3 fight with Ippo)
I'm not saying that it's impossible for him to get forced into a retirement. It's fiction, perhaps an alien comes down and grapes Sendo till Ippo begs to return to the ring... Just that based on real life (since the story is close to earth) and how the caracters were treated till now it's just seems very-very-very unlikely for me that Sendo's hand would be that bad.