Jazz (from the TFAverse, after the 3rd season finale) wakes up in an unfamiliar medbay. He realizes his joints feel rusty and stiff, he can't comm. anyone, and has no feeling beyond his waist. He manages to pull himself up slightly to see that his waist is slightly separated from his torso. The medbay door opens, revealing a strange green mech who looks at Jazz in shock, saying his name in utter disbelief.
Basically Jazz is bodyswapped with Jazz, but Jazz is dead so only Jazz wakes up as Jazz, but not as Jazz, an alternate universe's Jazz.
I mean, TFA Jazz wakes up in the previously-dead body of Bayverse Jazz IN the Bayverse, scaring the wrenches out of Ratchet.
That's the basic premise, but of course here's some things that could happen:
1. Jazz doubles over laughing when Optimus tells him he's the leader of all Autobot forces because: Optimus Prime, young maintenance crew bot, being a Decepticon-sized, deep voiced, battle-masked mech? Similar reactions to the contrast between the mechs Jazz knew and these new ones.
2. Prowl arrives on Earth to see a mech he thought dead walking around and cracking jokes. Also, Jazz hearing Prowl's voice and finding out that dear Primus, Prowl's ALIVE. In all, angst and shipping across 'verses.
3. Sentinel Prime is a jerk across the multiverse. What makes each Sentinel unique is HOW much of a jerk he is.