Dear, vector prime, two questions: 1. In the uniend cluster, megatron was often seen with a Cybertronian tank and jet alt mode, was he a triple changer? 2. What happened to him during his exile from cybertron?
The Megatron you speak of did indeed favour a tank alternate mode during the war for Cybertron, an adaptation of his original mining vehicle form. However, once the war took to the stars, he eventually began to favour the advantages conferred by flight, originally using a back-mounted rocket pack before undergoing a full rebuild into a Decepticon starfighter form. Along with being able to bombard his hated foe Optimus Prime from afar, this form was capable of long-distance space flight under his own power through the use of Dark Energon.
As for his ultimate fate, I’m afraid it is not an exciting tale. Megatron exiled himself to the long-abandoned fortress world of Chaar, cutting himself off entirely from the outside world. His spirit utterly broken by the realisation that he had become the domineering tyrant he had once fought against, he spent the rest of his days wiping all traces of Decepticon habitation from the planet. It is my understanding that a number of his former lieutenants made failed attempts to summon him back on to the Cybertronian stage; I believe if they’d succeeded he would have quietly ignored the message.
Perhaps this comes as a disappointment to you. Other Megatrons have made much more active attempts to repent for their actions. The one who captained the Lost Light eventually realised the unforgivable nature of his crimes and submitted to the Galactic Council’s justice. The Megatron of the OG World became a committed leader of the Cybertron Alliance and was indeed a hero of the downtrodden right up to his tragic end. But with his ideology destroyed and Optimus sequestered in the Realm of the Primes, he had nothing left. All I can say for sure is that, from what I can see of that universe’s far future, Chaangri-laar as it is known then is considered a paradise world for beast-formers.