I'm pretty sure that's all up to you to decide. If it doesn't feel comfortable anymore, then you should probably switch before you mess up your feet. But if you wore out the shoe to the point where you can see the insole, i think its time to switch. At that point you wouldn't have any cushion at the spot that has the hole.
Racquet : TGK238.1 2X / Head YTPP 1X
Strings : BHB7 17G 49lb / LUX 4g Rough 17G