When StealthSend is implemented will this coin go back to PoW?
stealthsend will be another coin exchanged 1 to 1 for stealthcoin
this two coins will exist simultaneously for a while and the exchange will be directly in wallet by what I understood.
Yes, stealthsend will be POW and will be worth a lot

How much it will be worth guess?

10k 50k 200k 500k?
Please answer
You want an honest answer? Check the distribution list for xst. Here is the link:
http://www.richlist.eu/stealthcoin47.8% to the top10 holders. None of them sells his position in the top10 not even now that the price is droping. If they continue to hold their xst coins the sell market will be very low and the price will sky rocket when a big announcement will me made. So think a function like this, many buy orders + few sell orders = price to the moon.
This coin will definetly see at list 20k sat.
Who do you think are the big holders? The XST devs team?
Note as well that the main holders of XST accumulated their XST coins in August-September - when the coin`s value was around 1K satoshi. So at this stage, they have nothing to loose.