Pub/Commuter Bike - Repair or Throw Away?

[v15ben]

I currently ride a 1999 (yes, really!) Giant mountain bike.
It was about £400 new all those years ago and still goes OK for an oldie.
I do about 200-300 miles a month commuting to work and messing on local off road trails/canal paths.
The chain just snapped after dropping it down some stairs, plus I need a new front tyre and it needs a service.

My question, much like with bangernomics cars is when should you give up spending and just buy something newer/better?
I need a daily mountain bike that I can leave anywhere, ride in all weathers and not care about too much if it gets scratched/battered hence using the old but functional Giant.
I'm wondering if I just spend the few quid for a new chain/tyre and service items or whether it's worth getting something new (or lightly used) to finally replace the old thing after 15 years faithful service.

TL;DR - my old pub/commuter bike needs money spent on it, I'm not sure whether to just spend a few quid on the parts or throw it away and get a new one!

[v15ben]

Seems to be a general consensus then!
To be honest, it would be like putting down a faithful family pet if I got rid of it now.
Probably a bit of "I want a new bike" syndrome going on here as well.
'Old Heap' lives to fight another day!

[v15ben]

Very true.
Think it was more a case of should I throw more money at the old bike or just put it towards another.
Far from terminal.
I can't see anything killing this bike unless I crash it/it gets nicked tbh.

[v15ben]

Well it is back up and running with a bit of tinkering at the weekend.
Managed a 40 mile ride with some big hills to boot as a reward for surviving the repairs!
There is life in the old thing yet.