I think Garp will die fighting BB or Akainu instead of Kaidou(if he's to die), to set em as PK lvl candidates for Luffy to surpass em.
For i dont think Kaidou need that big hype for Luffy to take him down, he already is WSC and fought BM on equal stand. Garp fighting both together won't set anything up for Luffy since he isn't capable of beating em together not here in Wano. Tho it will put some respect on Garp name if he dies fighting Two top tiers together and he's also connected with Rox pirate event. Bt i see no ulterior motive for Garp to die fighting em. It won't accomplish anything.
Or
It could happen that Garp will simply comment on BB, Akainu or Im Sama surpassing Rodger or previos era, when Dragon(who he believes is stronher than Prime Garp) is beaten by IM Sama, making him the absolute strongest in the World.