While having the ability to power a useless building to give at least half of its strength back I don't think it would be a great idea, or if it would even be possible but this does bring up a problem with adv base defenses and power.
While losing a power plant or adv base defense by themselves can be detrimental to the team: 1. Being the loss of base defenses(obv) or 2. The increase in price of all units/vehicles by %50. Losing the Power Plant when there are adv base defenses means not only the increase in prices but also the loss of defenses which means you are being punished 2x for the loss of one building.
Simply letting the offline building be destroyed isn't really an option either as it would give the other team an even larger vp lead and more credits, which means your team has to divert manpower to keep a useless building alive or risk being overpowered. One solution is to simply make the offline buildings give half the vp/credits from damage taken and from destruction, this way it makes the building less of a target and the other team cant just farm resources from it as easily which could help balance things out a bit.