I dont believe i can win Elleshar with small casualities if I use Xarfax. Is there anyway that i can fight vs Elleshar with my main hero ? Btw i have first visited the area and then retreat, I am over that phase.
By this point you should have some Ramparts under your control. Build them up all the way and accumulate troops in each. Use the main hero to ferry these troops to Xarfax who then engages Elleshar. If I recall right Xarfax MUST defeat Elleshar. Make sure Xarfax has picked up the nearby Pandora's Box and received the benefits within. If the fight still can't be won, pass a few weeks, gather more Rampart troops, and ferry them to Xarfax to try again. Save before the battle and try different tactics to see which is most efective e.g. targeting the Archers first or the like.