Cooked Sauerkraut is still healthy for you but when you do cook or can sauerkraut the heating of the sauerkraut does kill off the beneficial probiotics and bacteria.
The beneficial bacteria and probiotics are killed off and destroyed when the Sauerkraut is cooked and is heated above 106° F
If you're just warming the sauerkraut up a bit and not getting the sauerkraut up to 106 F temperature then the probiotics and beneficial bacteria will remain in the sauerkraut.
But still it's perfectly healthy to eat sauerkraut even when you cook or can the sauerkraut.
But sauerkraut gives you the best health benefits when you don't cook it or heat it up first.