Any way to revert killing kitava ?

I did kill kitava and complete act 10 last night. Now i realize that I am stuck with my maximum resistance penalty wherever I go.

I didn't saw any warning about that. Would be nice to have one.

Is there any way to return to the previous state ? Unkill kitava kind of thing ?

No. There is no way to undo it. Everyone gets the penalty.

You saw it the first time you beat Kitava? Guess you could use your deductive skills...

On a side note, I usually beat Merciless Lab before doing Kitava, exactly because of the resistance penalty.

It's something you get used to once you know it's happening. On my league starter for Abyss I've had my resistances overcapped for elemental weakness after Kitava before the end of act 9 (not like that's a lot of time considering act 10 takes an hour or two at most).

Why would you want to return to not being able to run maps.

Watch some videos on how to buy a cheap set of entry level mapping gear. You can do it in 20 minutes for less than 10c. ZiggyD has a video series that helped me alot when I first started.