All depending how much of the board is missing and what the circuit is, but you can just use thin wires soldered on to replace the missing parts. Solderable enamelled wire is an easy way to go, as the enamel comes off with the soldering iron and flux. No stripping needed. Tack it to the board with super glue or hot melt.
Also there are pcb repair pens that use a silver loaded glue, all you have to do is draw the new track.
Only time this could be a problem is if the board is carrying high frequencies where the board itself becomes part of the circuit due to its inductance and capacitance.
Of course it does not work so well for multi layer boards, I assume yours is either single or double sided, not a multi-layer one.
Edited By AdrianR on 14/08/2019 14:13:33