Ultimately yes, you will end up getting back across the border into the US even without a passport. The problem is how long it will take. I regularly cross the border in TJ, Juarez, & Nuevo Laredo & & have seen people detained, searched, & scrutinized for hours, one for 2days (he had a bad attitude) all because they didn't have the proper documents.
Think about this, you get held up at the border for 2-3hrs while they check your credentials. This causes you to miss your flight & now you have to reschedule paying a $150 rescheduling fee + the difference in ticket cost, say $200(believe me last minute tickets are more expensive). But wait, there's more!!! The next flight they can put you on isn't till tomorrow morning(Murphy's Law) so now you need to get a hotelfor the night.... Hmmmm.. San Diego, near the airport.... I'd say $150 is pretty conservative, & you'll need ground transportation $50. So, let's see. Looks like $550 & a lost day to me.....
Passport = Murphy Repelent