Typhoon's first operational deployment, Gordon Brown permitting, is to be to Afghanistan, and not in the air-air role... (and that is in the public domain)
Assuming that the programme goes as intended, then the strain on the GR4 and Harrier fleet will be alleviated by Typhoon in the AG role. Yes, the first AG fit is 'austere', but the term is rather misleading. Potentially, that could mean four PGM, two fuel tanks and a Litening III, which is less austere than some aircraft...
And if we bin the Typhoon, what do we replace it with? How much will re-training the pilots who've already done the Typhoon OCU cost? Ditto for re-training of those who service and support the type? What about the waste of money already invested in the infrastructure for Typhoon? Where does the money for infrastructure for and training on the new type come from? How long between disposing of Typhoon and the more useful new aircraft becoming operational? How much would clearing British weapons on the imported type cost? Or would we buy weapons the aircraft is already compatible with, adding logisitical burdens to the service? What would the implications for aircrew retention be as an aircraft that appears to be hugely popular with those flying it is withdrawn with the prospect of flying a less capable machine when it arrives (since it won't be an F-22, whatever it is)?
Getting rid of Typhoon would leave the RAF relying upon two aircraft types for air-ground work, one of which (Harrier) is likely to face fatigue issues that will have to be rectified at significant cost within the next decade; getting rid of Typhoon increases use and brings that problem forward. GR4 has an OSD of 2025; getting rid of Typhoon would potentially increase the burden on that fleet, risking a reduction of airframe numbers as the type runs out of life thanks to greater than predicted useage. So the plan would risk reducing the airframe numbers and the ability of the RAF to provide an attack capability.
Of course, if prepared to hedge that the US will make up the difference, or that we can be sure we won't need the missing capacity in capability until JSF enters service with the UK (now looking like the early 2020s), then the plan only represents a massive loss of money instead of being a huge risk as well.
By the by, the cavalry were awfully effective under Allenby in Palestine and the odd cavalry charge has been useful in Afghanistan (what's the Pushtu for 'Donkey Walloper', I wonder?).