Consolidation (at least when I did it years ago) involves two things.
(1) Your current open student loans will appear as closed.
(2) A new student loan will appear as open.
First off, these events could occur separated in time. #1 could happen first without #2 happening for another month or so. If so, then it will appear as though all of your loans have been paid off. (Unless you have some other open installment loan, like a car loan -- can you clarify?)
The Experian mortgage model doesn't like it when all your loans get paid off, and you could lose some scoring points for that. EX mortgage likes it best when your reports show some open installment debt that is mostly (but not entirely) paid off. For example, a 20k loan for a car on which you owe $1700. If that was your only loan, EX mortgage would love that.
But let's assume that both #1 and #2 appear on your reports this coming Tuesday. In that case, you have a new account that has appeared. That affects your Average Age of Accounts and also a factor called Age of Youngest Account. When your AAoA goes down that can hurt your score -- and when it looks like you just opened a new account (Age of Youngest = 0 months) that can also hurt your score. For the impact of AoY it depends partly on what AoY was before -- same for AAoA.
Finally, if the student loans were your only open installment loans, then your "installment utilization" will also have changed. That shows the percentage of your open debt that is paid off. When the old loans close and you have exactly one open loan (the new SL) you will owe 100% of the amount of that loan. If previously you had paid off a good chunk of your student loans, you will now be going from owing 30% (say) of your open debt to 100% of your open debt.
Knwing all this scoring theory, however, will not help you right now. It's just theories, ideas. You need something practical. The practical thing to do is wait until all the new accounts have changed on your reports, and then go to myFICO and pull your mortgage scores. That will tell you what kind of impact it had.
PS. Your lender may understand that this thing they asked you to do could change your reports and therefore your scores. So they may have an internal policy of going with your previous score if the only change that happens to your reports is the SL consolidation. I don't know.
