Having your suspension forks upside down is a good thing. It keeps the internal components like the foam rings and wiper seals lubricated. This helps to cut down on static friction (stiction) in use. Oil seals and foam wipers dry out and dry seals drastically increase friction inside the fork. Depending on the lower leg bath oil levels and service intervals, just riding and compressing the fork may not provide the optimal lubrication for the seals. It is for this reason that some suspension manufacturers and professional riders recommend storing your bike upside down.

You’ll have no problem with leaks unless you have a seal failure already. Compressing your fork due to trail surface impacts during riding produce far higher pressure peaks on the seals than turning the bike upside down.
Many forks like the current most popular fork on the market have no air inside the damping system. It is a closed system with a bladder to compensate for temperature and variations like some hydraulic brake systems. In this case the position of system makes no difference to its function.