For FSM ETF RSP, is it possible to terminate my RSP and still hold the ETFs or sell them at a later date?

Yes you can. Once you terminate the RSP, you are just informing FSMOne that you do not want to continue buying in the future. The shares you bought will still be in your portfolio. You can sell anytime but then your fractional shares cannot be sold. However, if you want to sell everything, you can request a Sell RSP transaction and they will execute them one business day after 15th of every month.