As long as the UK operate F-35 there will be a requirement to enhance and validate emergent capabilities through trials; therefore, 17(R) will continue to exist. The TES aircraft will be permanently based in the US and so will 17(R).
UK students will conduct their F-35 training at Eglin AFB as part of the Integrated Training Centre or ITC. Whether the UK goes ahead with forming its own OCU later downstream remains to be seen but I'm confident the intention is still there to do so.