The Mission Editor allows anyone to create their own missions for the game using maps from the base game or maps made with the Map Editor. If you lose your tank in a fight, you’ll need to bring your crew (or what’s left of your crew) back to your lines safely on foot.
For example, while the main objective of the greater team may be to conquer a specific area, a sub-objective could be requesting a tank to clear its way from an anti-tank gun that has been sighted, or getting your squad to take out that anti-tank gun yourself.