Coletherm insulation

If you're going to remove the old insulation, it's a fair amount of work. Synthetics were sewn to the shells, usually every foot or so, so there are a lot of stitch lines to be ripped apart to separate the insulation.

That raises the question whether the insulation is of any particular value, and so worth going after. Many of the synthetics on the less expensive bags were not very valuable to begin with, and with some use and a lot of stuffing, lost a fair amount of loft.

If you are going to put some work into making a quilt, why not start with the best quality insulation available, so your work will be well spent.

On the other hand, if you're just going to convert the old bag into a quilt, as your reference to not buying ripstop suggests, consider the current weight of the bag, and how much you'd lose by removing the zippers and whatever else you'd remove. It may be so heavy compared to what a new quilt would weigh, that the outcome would not be what you want.