It is hard to predict just how much damage lightning will do to an oak tree. The outward damage is obvious, like a burnt off limb or the bark blown off.
Burnt off Limb
If your oak tree is still standing even after a limb has been blown off by lightning, that's a good sign. The tree will likely survive if the limb absorbed the brunt of the lightning's force. In this case, you will only have to do some light pruning to reduce and balance the weight distribution.
Less Obvious Damage
It may be difficult, but often times the best thing you can do is wait and see what happens when a tree has no obvious injury after being struck by lightning. The tree might recover on its own or parts of it might die off and need to be removed. Sometimes a tree that appears to have sustained a lot of damage will end up being just fine. Oak trees have good energy reserves and can often recover from serious injury in just over a year or so.
It is always best to wait before taking action with a tree that has been struck by lightning. If you are worried about your tree, talk to a tree surgeon and see what they think. They will likely tell you the same thing, just wait and see.