Monarch are a respected company for both their airline and engineering within the aviation industry. They would not risk any of this by using an unsafe airline.
Serenity, I agree with you completely!
However although this incident is relatively trivial the media coverage with passengers saying "It's the oldest aircraft I have ever travelled on" will not be good for Monarch's credibility.
It's one thing for an airline to meet the minimum regulatory requirements but another that they are who one would choose to travel with!