Question: The link between brain activity and qualia is unexplained. But most people think the former causes the latter.

What if its the other way, that our mind creates the external universe?
This does not necessarily mean that all other people are without a mind.
They also could have their own consciousness, but when they pass through this reality, we all create a 'Graphical Use Interface' which constructs a mental model. Our brain is part of this model, so when we die there is a possibility that our model of the world has died, but we have not.

Is there a way to eliminate this possibility?

(because this thought is unsettling; that I have to live through possible eternity)

Answer: 
Yes. You can eliminate that possibility.

First of all, what you are aware of as being "you" is the experience of being you. This is clearly separate from what you experience as external to yourself, because you aren't aware of creating things that you perceive as external to yourself. Could this generation of things be coming from some part of "yourself" that you are unaware of? Sure, in fact, let's assume that this is the case. We have at least two parts of you: the *experiencer* and the *generator*.

So you're asking about whether it is possible that this part of "you", the generator, will shut down, but the part of you that is the experiencer will keep on going? This doesn't make much sense. It seems far more likely that the generator (which may also create other experiencers like me for you to interact with) will keep going. After all, the evidence suggests that it was already here before you became aware of your experience.

But let's say it does happen, the experiencer continues and the generator shuts down. Well, now the experiencer has nothing to experience. Time is generated, so there's no time, space is generated, so there's no space. The experiencer won't even be able to think thoughts because there will be no experience of time to think them in. So there's no sense in which the experiencer will continue forever, because there's no longer a forever to continue into.

You could argue that there's some sort of external time that isn't being generated by the generator, but now you've broken the central premise that our minds generate external reality.
Assuming [mind-body connection as holding true](https://philosophy.stackexchange.com/a/93309/14508) (mind and body are connected, regardless if "mind" is an epiphenomenon of matter or a separate thing in itself) and assuming matter-energy to be conserved, we can infer mind, in some sense similar to matter-energy, cannot be lost as well.

But this does not necessarily mean that a mind is conserved in its initial configuration, similarly to how matter-energy is conserved but not in the same form and configuration.

So what happens to mind after death? Noone knows! No matter how one argues for something or its opposite, etc.., a degree of speculation cannot be avoided anyway. But if above reasoning can be true, mind is not lost, although it is possible mind does not retain its original configuration either (eg identity). So in this sense, "I" that we know during life is not necessarily there after death, although "mind" as a substance may be conserved and not lost after death (in the same manner as matter-energy).

A somewhat similar perspective is phrased in the Buddhist *Tibetan Book of the Dead* in that it describes how mind changes and disintegrates into other states (along with similar changes in the body) and how one may choose which path to follow, but this "one" (according to this answer) is not necessarily the same or comparable as the one's "I" during life.