Eventually (if not already) They will do the same as what they did with CCR. Although slightly different as CCR was the most reliable train ever, they looked at the amount of guests each year tallying against the yearly cost, it was ran by diesel so it wasn't the cheapest with rising fuel costs and was eventually decided that it wasn't justifiable to keep it running.
They will look at Slammer and go, ''oh we are spending hundreds of thousands on this contraption, and the throughput is pitiful with only 6 (being the average) cycles being sent an hour. We get barely 200 people an hour on a busy day we have to close it once or twice a day to do routine maintenance. Do we really need a sponge of a ride that sucks in every penny from our budget to be closed half the season with barely anyone riding it? Simple answer no''
Slammer's time at the park is VERY limited with a yearly pattern of being closed half the year particularly over their busy periods being Summer and most of Fright Nights. Yes it is another ride that can (as some may put it) 'Soak some of the guests up'. But if they closed it and got rid of it those hundreds of thousands of pounds can be put into fixing other rides promptly, so all other rides can be on maximum capacity at the best part of the entire season.
What you have to think about is whilst Slammer continues to piss everyone at park off, cuts are very likely to be made to other rides. Heck, Zodiac had 4 carriages off most of the season last year, but I'm sure if they hadn't sunk money into Slammer that money could have been used to buy new mechanisms for the doors on Zodiac.
The sooner it goes the better from an engineering point of view.
And just to clear it up, Slammer is actually my favourite flat ride at Thorpe Park.