I know that Nirvana is not like heaven the one they have in Christianity and Islam, but rather just a state of mind in the present world. Then what happens to someone who dies after becoming the enlightened one or becoming a Buddha? Where does he/she go?
According to my understanding of the Pali canon, that (i.e. "Where does he/she go?") might be a tricky question to ask of the Buddha even when he's alive (or have an unexpected answer): see for example the topic, Why is the Buddha described as trackless?
Also a classic understanding is that birth is equated with suffering, and enlightenment is equated with no further birth (see for example the comment about the "house builder" on this page): so maybe there is a concept of an after-life in Buddhism (see also Samsara) ... but not for the enlightened Buddha!
On the other hand, Nirvana itself is described as Deathless.
There are 2 types of Nibbana which are:
- sopadhishesa-nirvana (nibbana with a remainder) - while alive
- parinirvana or anupadhishesa-nirvana (nibbana without remainder, or final nirvana) - after death
Nibbana is being blown out. So once you die for a person who has attained Nibbana does not go any where. The person is extinguished. This is like when you blow out the candle the flame does not go any where. The conditions for combustion are not there hence it extinguishers. This is similar to Nirvana. Conditions for future rebirths are no longer present hence you get extinguished.
I start answering these things and I want to pull out a bunch of references and quote books etc.... Then I think "thats just ego if I dont need it to answer". So let's try it this way.
Yes, most definitely an after-life exists in Buddhism. We are not really this body. We are the drivers inside it. NOT the brain though, thats physical. That preserves memories and identifies patterns. We are the actual feeling part of the emotions.
So we have this shell of a body that dies. It doesn't come back. Inside we have the driver, our consciousness, and it doesn't die. Truthfully it was never an individual. Our consciousness is part of the consciousness whole ... which is subject to all of the feelings of the universe and not just our crappy little 5 senses. Our awareness is limited to this vessel right now. A limitation that goes away as we return to the whole.
Once our bodies die we just keep doing this same cycle of crap until we ascend dimensionally.