If they're legit mildewed, they might be ruined. The mildew can literally eat the canvas and the weave gets loose enough that you'll never be able to waterproof them again. A little musty smell will dissipate if you set the tent up and leave it to air out, but if it's got a proper funk to it you'll need some elbow grease to bring it around.
This is the wrong season for this, but watch the forecast for a nice long sunny stretch and set it up in the yard, full sun. What would take 24 hours in the summer is probably most of a week in the winter, but you need it good and dry and the mildew does not like the UV at all. Go over the canvas inside and out with a dry bristle brush to remove any dried mud or loose whatever, and vacuum it up. Then to kill any mildew that might be lurking, spritz the whole thing heavily inside and out with a 1:1 of water and rubbing alcohol. Pay attention to the seams, get those good and soaked. Let it get mostly dry, then go after it again with a soft bristle brush and soapy water - a mild dish detergent is great. Then you're ready to reapply the waterproofing of your choice and she'll be good as new.
Unless they're actually rotten I would hate to see you chuck them too. If you decide not to revive them yourself I'd love to take a swing. Old Springbars are awesome.
