Filed ITIN for spouse along with tax return. ITIN is still pending, but my husband received SSN. If we rescind ITIN application, what will happen to our tax return?

It depends.  The IRS will not necessarily input his SSN into the return, but it is possible that they may deny the ITIN because he became eligible for the SSN.  If that happens, you may input his SSN into the return and re-file.  (It may be possible that the return could even be accepted electronically, and that your return can qualify for Earned Income Credit).

It is prudent to wait a little longer, however, because if the IRS processes the ITIN, you will want to amend the original return to his SSN instead of the ITIN in order to receive the greatest benefit for your return, but also so that any Social Security and Medicare taxes your husband paid can be applied to his Social Security Number.  If you do need to amend the return, this FAQ describes how you may do so:  https://ttlc.intuit.com/replies/6603004