Please, clearly the "reinfection scare" is based on getting it again within weeks.

Immunity doesn't always last a lifetime, but often does with active immunization, and most definitely lasts years.

If we want to get technical about the immunology, of course you can get infected again.  With anything you've been infected with before.  The immune system doesn't stop the virus from entering your body.  The point is that if you have immunity, then you'll never experience symptoms because the infection will be controlled practically immediately.  Basic immunology.  If this isn't true, then you didn't survive the first infection.  Why?  Because only adaptive immunity can clear viral infections, and by definitition, this is where you develop immunological memory.

"No one knows anything for sure"  Come on.  If we are talking about the same virus (not a new, significantly different strain), nobody that survived a first infection has to worry about a second one any time soon (decades).  

This virus isn't infecting immune cells, so no trickery there.

If you are immune-compromised to the extent that you can't develop a good adaptive response and memory, then you don't have to worry about a second infection because you're dead.