If you reuse C-41 bleach and it some how is exhausted you can always rebleach again with another batch but fresh bleach. To reduce the impact of PH changes carried over by developer you can set up two bleach steps. One with an old batch of bleach and the other with a fresh one. If the first batch is so exhausted the bleaching will be completed by the 2nd batch.

To oxygenate bleach I usually fill half a bottle of it, cap the bottle then shack it vigorously for 10 seconds. It will form a lot of bubbles but the bubbles will disappear quickly by shaking the bottle again but only lightly. You can repeat it one more time if you want. The bleach is usually recovered quickly this way for me.