As a footballer match fitness only comes with playing games from the start and playing for as long as you can, this brings the sharpness that you expect to see as well. Playing a player for 15-20 minutes will not get him match fit nor will it get him sharp so for me Hayes has to start next week, he gave enough today that shows he is naturally fit after his injury and will be 'match fit' very soon.
As for changing things for next week, why?
Yes the second half was poor but remember we were playing Celtic and they are always going to get chances and be on top for a period of time, lets focus on the positives and move on from there. Changing a backline after 1 game won't help either and the understanding will come over time, give them a chance to gell.
I would have been more inclined to change things if we had been playing St Mirren or Hamilton and gave them the number of chances Celtic had and let them play the way Celtic did in the second half.