Trying to settle Stafford Loan

I finally worked out a verbal agreement over the phone today with a collection agency to settle some old student loans that I neglected.

They were very old and very neglected. The settlement offer was 100% principle, 50% interest and no fees/penalties.

After they gave me their offer I told them I would call them in a day or two confirm that I could free up enough money to settle. If I couldn't come up with the lump sum I said I'd work out a payment plan when I called back.

Are there any "gotchas" I need to look out for when working out a final written lump sum settlement? If I settle now will a typical settlement arrangement cover a cosigner? I don't want to work a deal just to have them come after a cosigner for the forgiven amount. I had my first loan when I was only 17 and it had a cosigner. Sorry if this has been answered before. I didn't see it.

I expected a payment plan offer. I didn't expect them to make such a helpful offer. It's worth it to me to borrow money elsewhere to take their lump sum offer. I'm saving over $15,000 if I can free up the cash elsewhere to take their offer. I know I'll have to pay taxes on the forgiven amount and it will show on my credit as a settlement. Anything else I need to consider?

Thanks