Since Oda showed us that Garp was going to BB Island I've been reading a lot of guesses saying that Garp will be defeated by BB and Coby will be the next Garp, but that's so obvious that it just makes me think that it will be Garp the one who wins their next battle.
My guess is something like this:
Garp and BB fight and Garp ends up being victorious but somehow(or by someone) Blackbeard manages to escape and he is not captured, later on the series when absolutely no one expects it Blackbeard appears again doing sneaky things like he has already done back in the past(maybe even killing Garp in this moment).
Blackbeard is a character that has always been like this, a sneaky bastard that does thing no one expects. He literally defeated Ace to join the shichibukai to find a way to enter Impel down to recruit new members and then went to Marineford to kill Whitebeard and steal his devil fruit.
I don't like Blackbeard because of his strength but because of how sneaky he and his plans are. Of course this doesn't mean he is weak, he has been hyped enough by Rayleigh and he will most likely defeat Law but this doesn't mean that he has to defeat Garp right now.
I'm saying all this now because of the thing of "I need a hero" redon posted, i hope it's about Garp and we will see a conclusion about this thing soon.