I am not sure exactly which if the higher techs you need to solve the puzzle requiring your master builder.....but I think you may be lucky enough to be able to solve it even now.....with a little nudge in the right direction. WIth a 65 yo builder, she should last a few more years anyway, assuming you manage to keep her healthy
If you want that little nudge, feel free to PM me ..... be warned though, I am in Australia, so may only see your message too late for your builder!!
Savi