Rebuild or Replace?

Where's your problem, what parts is it that you have trouble finding?

A net search has the Giant Iguana down as a MTB, with a 3x7 drivetrain.
All the drivetrain parts are still readily available, as are 7-speed shifters - albeit not the nicest models.
Same with derailers. Rim-brake wheels haven't exactly gone scarce yet. Add a spacer and a 8/9/10-speed shimano-compatible wheel will happily accept a 7-speed cassette.
Brake pads, even if you have canti brakes, are readily available.
In short, I can't see any compatibility issues with keeping the bike in working order quite some time yet.

If you really have kept on top of upkeep, I see no reason why it'd make financial/practical sense to write the bike off now, or even the next few years.
If you're looking at a backlog of several items that needs replacing, then the cost of an updated drivetrain can certainly be a significant part of the cost of a new bike.
But simply keeping it rolling in its current configuration shouldn't be prohibitive(depending on the number of parts needing replacing of course.)

The model you are telling is widely available. So, you better try it on interesting browser or you my get personal sharing from some friend
🙂

Enjoyyy
Happy Riding

Why replace the whole system? Why not just replace the offending part? If the rear derailleur is the one messing up, then replace it and it only. You start going into STI briftors etc and you could be laying out some cash.

Yeah u can visit some relevant shop foh sure and check what they sayl...........

But again its up to you 🙂