#!/bin/bash

foo='  HELLO \
		  REDANT=${M45234}${CM_D33D}C \
		  MOREF=${C333M_V453451}${C33M_ERJE}'

echo "$foo" | sed -r '{ :s; s/( )? *\\ *$/\1/; Te; N; bs; :e; s/\n//g }'