My grandmother died the same year. I left the heating on 24/7, set to around 11C, IIRC. I also left the loft hatch slightly open so some heat would go up there. The ballcock valve did freeze (the ice broke the plastic inside it, so it let through a fast drip when it thawed, which went out the overflow which the neighbours noticed), but no other damage happened. After that, I also turned the mains water supply off in the street. The heating header tank did very slowly go down - I ladled some water across from the storage tank with a saucepan every few months to refill it. Also, open cupboard doors against outside walls if there's any pipework in them, to allow the heat to reach the pipes. Otherwise they may be in a cold spot and still freeze.
It took over 2 years to get probate and sell the house, so the house was left running like this for some time, but I did check up on it every month or so.
Note that in an older house, you are likely to need a warmer temperature to prevent it getting damp than you are just for the frost protection.