"And what if you need two go-arounds?"

Easy: you don't try the second landing approach before the battery is sufficiently recharged to contain enough energy for the second abort. Chances are this does not take any longer than going through the pattern anyways.

The saving is not just the dead weight of the bigger engine you'd need to do take-off, climb and abort without electric assist, it's also the fuel saved during cruise from running an engine that is completely designed for efficiency at cruise load instead of for some compromise between cruise efficiency and sufficient peak power for start and abort.