Doing my tax return and being asked for info about my late husbands income and his terminal tax return has not been filed yet, now what?

I am sorry to hear of your loss.

When you don’t know your spouse’s income and can’t find out through reasonable means, the CRA recommends that you enter your best estimate.

Here is some more information regarding preparing returns for the deceased: https://turbotax.community.intuit.ca/questions/1189877