Warner's replacement at SRH i think is fairly straight forward too be honest - they need an opening batsman as a replacement so that means quite a few options Guptill/Hales/Ronchi - i think the new captain will be squeeky clean Kane Williamson.
Smith's replacement however i think is more tricky as there are less middle order bats for RR to choose from and i think like Manor says they will be reluctant (or may still do so) go for Root because of his availability (and don't forget they lose Stokes as well at the end and maybe before that!).
Also consider who RR have already got as overseas - Stokes, Archer, Butler, Short and Laughlin - Smith was guaranteed to play as captain but now Rahane is captain they may go for an overseas that is 1. available the whole tournament and 2. that is a back up eg. Lendl Simmons
People saying Amla for a replacement - he has committed to being Hampshire's overseas for the 1st 3 months of the season so i think that probably runs him out.