I play the Dark Side. I have Orbital Bombardment in play (+1 Objective damage for each attacking unit) and attack my opponent's objective (5 damage resistance, 1 existing damage) with a Fleet Navigator (1 Edge-dependent Tactics).

My opponent declares his X-Wing Escort as defender.

I play Backstabber and deal one damage to the engaged objective.

I win the Edge Battle and use the Fleet Navigator to focus the X-Wing Escort and deal one damage to the engaged objective.

I then deal 2 damage to the objective with Backstabber, destroying the objective. Since I'm not interested in the Unopposed Bonus, do I then also have to deal Backstabber's two Unit damage to the already focused X-Wing Escort, thus destroying the Escort and my Backstabber since it's the only Vehicle I have in play?

Yes - It doesn't matter if you have a valid target or not, if you focus to strike you have to resolve ALL your icons

if there is no valid target, nothing happens

if there is then you must resolve the icons