You know, just because something wasn't mentioned again, doesn't make it a loose end. Many of the stories on Stargate were self-contained and need no resolution.
Jacks wife and father in law
Fire and water alien
What fate awaited narim
the aliens from prisoners
the aliens from gamekeeper
the aliens from scorched earth
the message in a bottle aliens
hippies from 1969 did the guy go to war
jacks friend from evolution
None of the above constitute a loose end, because they did all they were ever meant to do. What would be left to tell with Jack's wife and father in law? And Narim, Urgo and Harlan just...went on. None of them was ever likely to set the galaxy on fire. Catherine's niece was less than that, never more than a plot device, and Emmet Bregman came and went; there's no reason for him to turn up again, no unanswered questions to address. Likewise Urgo, Jack's old friend or the hippies; what they went on to do with their lives is unimportant to the Stargate story. Cassandra could come up again, but doesn't have to. It is perfectly valid to assume she's just going to college like any normal Earth-girl.
These are recurring characters. Dr Lee has no existence except as an adjunct to SG-1 and Maybourne was left sitting pretty on his own private planet. What's left? If they did mention Maybourne again, it would probably only be to say that his planet was destroyed by the Ori as well.
the inhabitants of abydos
Oma and anubis's fight
lord yu's first prime
None of these constitutes a loose end, because they're done. The inhabitants of Abydos are gone, Oma and Anubis locked in an endless struggle which could only possibly be trivialised if it turned out that 'endless' meant 'for a couple of years or so' and Yu's FP was with him when he was assassinated by the Replicators, so he's almost certainly dead. Just because we didn't see him die doesn't make it a loose end.
the ninth chevron
is not a loose end. There are nine chevrons for purely aesthetic reasons and it's only fan imaginations that really attach any significance to its existence. Not that I'd put it past them to end the series with SG-1 stepping through a funky, nine chevron wormhole to infinity...and beyond. (Only hopefully not Stargate: Infinity).
For there to be a bona fide loose end, there would have to be a question posed by the episode and not answered; and not merely 'what happens next', as almost all stories (Michael Moorcock's Stormbringer leaping to mind as the obvious exception) leave the protagonists with the rest of their lives to lead.
So, genuine loose ends might include:
The Furlings - what gives?
Rya'c and Bra'tac - they have been too central to the Jaffa stories not to get some last mention.
Kinsey and the last of the Trust - Since he is explicitly still out there, this is an issue to be addressed if S10 is to bring closure.
What fate Langara? - they won't do it, but I think they should.
Daniel's grandad and the giant aliens - he was supposed to be learning from them to bring knowledge back to Earth, after all.
There are a few others it might be nice to see, but which are quite happy as they are:
Teal'c and Ishta
and...well, other relationship issues which are not a high priority, but it might be nice to see them closed.