Why would they get an IRI? Its a stand alone rating, they already have a FI rating with the privilege built in except that without an IR they will not be able to teach for an IR. If the IMC rating is retained in the next round of EASA talks, then they may be able to continue with their existing privileges; the answer is as yet unknown.
The built in IMC privileges do not exist under EASA but your UK ATPL will still be valid on an Annex II aeroplane.