Of course, I don't absolutely think that he had any real inkling that he might actually and literally die while fighting Drago. But still, part of me thinks that when the time came for Apollo's demise, he would've gladly chosen the option of "dying with his boots on" rather than getting old and feeble. I obviously got that sense when he got upset at Rocky for telling him about changing into a regular person. I would like to believe that in Apollo's mind, challenging Ivan Drago (especially in the middle of the Cold War) his way of defending America's honor.
I think Apollo (despite his friendship with Balboa) was a bit jaded with being out of the limelight for so long. This fight (despite being billed as an 'Exhibition') was anything but for Creed. He went full-on with the 'hype' for the Drago fight and then had to live up so such big words.....and possibly (given the timeframe) actually believed the whole 'US-Vs-Them' mindset (that this movie was striving for)
He likely thought that he could (as with the previous Balboa bouts) go the distance, give his all and overcome Drago. However, by the end of the first round against the Russian....he knew that he either had to put up or shut up (quite literally) and took the inevitable 'suicidal' route. To be fair, given his ego (and braggadocio) he'd have likely perceived himself as a laughing stock, had Balboa either stopped the fight. In my opinion...he'd have likely blown his brains out, had he survived the Drago fight, anyhow?
That is a great question. I think like a lot of professional sports people that live and breath their sport for so long with training and competing, when you retire it can be something of a shock to you. Finding something else in your life that can fill that void can be really challenging and more so if that is what you are really only good at.
While Apollo retired, he also retired knowing that if it wasn't for Rocky he may have gone on for longer as champion and this really got to him. In the fight when they could have stopped it, Apollo should have accepted defeat but like seagal72 said his ego ultimately was his downfall.