It depends a bit how you feel about the car yourself - if you are happy with it, and are reasonably confident that apart from the head gasket, the car is otherwise sound, in good condition and likely to be able to give many more years of service, then it is certainly worth repairing.
If you are able to carry out the repair successfully yourself, it is more expensive in your time than it is in monetary cost, so needen't be a major financial outay.
There are a number of mechanics (both with fixed premises and some who are mobile) who would be recommended by forum members to do the repair for you, but I see you haven't put your location on your forum profile, so it is difficult to make any specific recommendation as to where you should go.
One set of mobile mechanics who are highly recommended and will travel just about anywhere in the country are Home -- MG Rover Mobile Mechanics
who are based in Derby - a straightforward head gasket change on a non-VVC K series is £320 plus the cost of fuel for them to travel to your location.
If you decide not to have it repaired, I would suggest offering it for sale as spares or repair first off - the value of these cars, and the low turnover of parts from brakers now that their numbers are dwindling, and many people don't even bother repairing them when they go wrong means that you will be lucky if a scrappy will pay you more than a few pounds for it, and if you break it yourself, you will find some commonly needed parts will sell quickly (at the right price, not the astronomical prices that some ebay sellers seem to think they are worth), but you are likely to be left with the majority of the car untouched; you will then find that (having had the sellable/valuable parts removed) a scrappy may not want it at all, or may charge you to take it away.
If it were mine, in good condition, and I was planning on keeping it for some time to come, I would have it repaired. If done by a reliable mechanic who is used to the K series and knows what they are about, there is no particular reason why the head gasket should fail again.