How was there still enough air-pressure inside Mark Watney's suit even though it was compromised? Do you think this is possible?

It is possible.

Explanation:

There is still enough air-pressure inside Mark Watney's suit even though it was compromised because of the presence of huge amount of air in the suit of Mark Watney. When he tear his suit in order to move upward to reach his crew member, the suit lost some amount of air but not all the air is lost so we can say that there is still enough air pressure present inside Mark Watney's suit.

answer conditional instability;