I have Autism and have dealt with a death of my own recently. My sister passed away the day before Thanksgiving, and at the time, it wasn't hitting me all that hard. I already knew that it would take time for the reality of it to sink in, even though I was completely aware of what had happened on an intellectual level. Fast forward to just a few weeks ago and the whole thing hit me like a ton of bricks. I felt as if my heart had been frozen with liquid nitrogen then smashed with a sledgehammer. I know that people with this condition, along with milder forms of it, find comfort in solitude from time to time. No matter the reason, it helps us reduce stress on our minds by cutting out any extraneous stimulation that we may live with. I do believe that Aspies are more spiritual than most - or at least I am. Even so, for whatever reason, the sudden shift in the scheme of things can be detrimental for somebody on the spectrum. And when somebody whom you were very close with isn't there anymore, it can be a very hard thing to deal with. Imagine if you can, a rat going through a maze with the goal of finding the cheese at the end. The cheese is the rat's reason for even figuring out the maze. Now imagine that when the rat finally finds the cheese, one of the scientists decides to stick his hand in and yank it out. The rat feels as if the very thing he set out to find has been taken away for no good reason. That's kind of how Autistic people deal with death, or at least how I do.
Now, when it comes to grieving, that may be more of an excuse to make a retreat into that inner dimension many people on the spectrum are known to do in times of what we perceive as a crisis. There is a comfort there, a warmth that we need to embrace every so often in order to keep us as sane as we can possibly get - especially in trying times.
I hope I was able to shed some light on your situation.