Bugenhagen's second ability checks at the moment it would trigger to see if you control a creature with power 7 or greater. If you don't, the ability won't trigger at all. If it does trigger, the ability will check again as it tries to resolve. If you don't control a creature with power 7 or greater at that time, the ability won't resolve and none of its effects will happen.
Reach
At the beginning of your upkeep, if you control a creature with power 7 or greater, draw a card.
: Add one mana of any color.