Actually, they believe that a select group of 7 million JWs make up the 144K that go to heaven. The rest of them live forever on the earth.
I remember ‘studying’ with JW’s long ago, being raised an atheist, I didn’t know better.
Anyway, they believed that the 144,000 were special chosen from among their ‘church’, and at that time, the 144,000 ‘spots’ had been ‘taken’. This was late 1970’s early 1980’s. They also believed that when those 144,000 had died, the millennium age would come.
I was lucky I didn’t become a JW. I had known about an early prophecy of theirs, and asked for the ‘study book’ from that time. I found their prediction, and then knew that they weren’t true.
It much later that God convicted my heart and I accepted Christ.