In Shinto (which I should say I'm not technically a believer in, but rather a member of a shrine), the idea accepted by the Jinja Honcho (Shrine Association) is that when people die, their spirits move onto an 'otherworld' which is a neutral place exactly like the living world, except that it's populated by spirits and kami as well. There are possibly several but none are heaven or hell and its disputed whether you can influence where you go. This will happen to everyone regardless of how much you worshiped the kami or ancestors in your life. You don't have to believe in kami or spirits or any god at all. You just go there, new life, boom.
However I guess you could argue that being a part of Shinto (or rather a family that practices ancestor worship) does matter because it's worship and veneration that allows and ancestor to watch over the family in the living world. So anyone who has family who worship their ancestors may be able to gain power over the living realm in order to protect your family. So, I guess that non-believers will likely never get that chance, so believers and nom-believers don't have an equal experience in the afterlife.
I should say that this really doesn't matter though. In the end, the only difference is whether or not you will get whisked away to the living world to serve the living or not. It's not necessarily a pro or a con unless you have strong feelings about how you'd like to spend your time in the otherworld. Do you want to be useful to your descendants or do you want to retire?
Anyway, this was a fun question to think about!
I've never known a Shinto practitioner on RF! Hi, thanks for being here.