Al and Cal, the Nerbs, Thorny, Betty Butterfly, Mobie the Cavebear, Larry Lynx (and co), the Iron Queen, Fly Fly Freddy?

Didn't Fly Fly Freddy become robo'd and died'd from turning into a pile of scrap?

As Jenna-Lu was only ever shown in flashbacks, she probably is supposed to be dead--unless that "old" lady that appeared a couple of times was supposed to be her. I still think that if she really was supposed to be alive that Knux would've met her in a way that we'd know it for certain considering all the other relatives he met. But hey, she, like many other characters, have totally unknown fates.

You could look at Fly Fly Freddy that way. They were supposed to put him back together. In which case, if they ever did, you can assume he's alive somewhere. It just depends on how someone chooses to look at it. I seriously doubt anyone is going to be spending time on Fly Fly Freddy to explain it. Though I guess if he were ever just put in a huge crowd scene that would be enough of an explanation if they wanted to say that he's alive. ;p

I actually asked Ian Potto about some of these characters back when "Ask Ian" was still in effect on his forum. Here's what he said:

I asked:
Also... did Valdez die when he got drowned/exploded by Espio? Would you ever consider bringing back some of the past robians that never appeared again once everyone was deroboticized? (Valdez, Freddy, Liza, Crystal-La, Carl etc)

Ian Potto wrote:
Valdez I believe was destroyed/rendered inoperative by Espio.
Liza became a Robotropolis robian. Hopefully she was among those rescued before Robotropolis was nuked.
Crystal-La, I believe, would have been deroboticized by the Bem and found her way to Albion.
Carl was possibly destroyed.
Freddy was probably repaired and Bem'd.

None of them are going to come up again any time soon.