Who promised you the tradeline would be removed? The original lender? If so, I would expect that to happen in the next 60-90 days. Not all lenders remove the old tradeline (and therefore, all of the lates leading up to the default) entirely, but generally, those who promise to, follow through on that. If you don't see an update in a few months, it would be good to contact them and explain what you were promised and ask them to make good.
The new tradeline for your rehab'd loan will be backdated to the loans original start date, so you don't have to worry about a significant impact on your AAoA.
I defaulted on a US DEPT student Loan so they sent the account to a third party to be rehabilitated... I am done with the rehab, just waiting for another servicer to pick the account up.. This account is my second AAofA. Should I request for a GW or leave it as that... BTW they had promised me previously that they will take the TL off as soon as I am done with Rehab..
I wouldn't worry about the AAofA. All of my defaulted accounts wtih DOE were deleted and that severely affecfted my AAOA but 30 days later my new provider (Great Lakes) reported and back dated to the same date that the DOE had before they deleted so in essence I gained everything back that I had lost.
I have heard people had problems with the original servicer of the accounts before DOE took them over (when they went into default) removing their tradelines. I did not have that problem. My student loans were in default for 7 years so all of those had aged off and I only had the DOE accounts reporting negatively.