It's possible for the panel not to kick back in , and also it doesn't really matter to be honest almost everyone who doesn't service there system yearly has this issue of similar types there's nothing an engineer could do to make your alarm not come back on unless for example there's an engineer's reset required
Being a house basher it sounds about right
Regardless of power outage I would do the same change batteries in sensor and any others that need it
£450 is cheap for the system
And £104 for the repair is a very good price
Looking at that frame it's messed up, you could drill in and out from the chamfer if your going enough
If you ever remove the contacts which I doubt you can always have all the upvc repaired these days but if it's your windows you can do as you need to
www.upvcdoctor.co.uk
They normally charge for a set of windows in the big scheme of things it's cheaper than trying replace or bodge it yourself
Or similar companies that was an example
Seems your exit our at front door is permanently open circuit , could be cable or the detector hence beeping continues even when you get back I assume?
You want to get an engineer to fix or yourself?
Wait for galaxyguy and some others I used to fit them not anymore, not because it's rubbish mind you
Have a look at selfmon aswell you can contact them to see there app options and what you can
Mr galaxy might be on holiday , we need notifications when posting names might nudge him
Geezer come you want to do all this protocol stuff ? Googling is easier
https://www.security.honeywell.com/uk/products/intruder/control-panels/galaxy-flex/462175.html