answered here too
when will they return??? Arjun and Purvi were briefly shown to be in Australia (in March) for Arjun's brain tumour treatment. They're still there and Arjun's treatment is still on, as mentioned by Manav a couple of weeks back.
The actors portraying Arjun & Purvi - Rithvik & Asha have quit PR and we have no idea if the CVs plan to bring the characters back with other actors. Given the number of characters they keep adding, it's unlikely they'll be back, but this is PR so :/