The Ahom people no longer exist as far as I know. They've pretty much been assimilated into the local population of Assam. They originally arrived to Assam in small numbers, so it only took a few generations to assimilate them into the local population.
Lachit Borphukan is mostly famous for halting the Mughal Emperor Aurangzeb's eastward expansion at the Battle of Saraighat in Assam. If Borphukan hadn't won the battle, then Aurangzeb would have eventually expanded into Northeast India and probably even come into conflict with Burma and other nations in Indochina. If you want to find out more about Lachit Borphukan, then it would probably be best to start with Wikipedia:
http://en.wikipedia.org/wiki/Lachit_Borphukan