What do you want?

To arrive in PHX as close to your original schedule as possible, or maximisation of TPs?

You mention this is a TP run, therefore I will assume maximisation of TPs if the priority.

I would just go with it - I am assuming you are in HEL right now anyway, so just go to the airport as normal tomorow since AY could pull in another aircraft to operate on time (it has happened before on this particular sector). In any case, getting to LHR should be the priority since you will have infinitely more options from there. You could ask to be routed onto the first BA service of the day (if there is space), and you'll meet the rest of your schedule no problem