I would much prefer him not to have been injured and wish him a speedy recovery. God knows we need all the options at the moment.However, I think most people agree Petrov isn't a long term midfield option so at least we now have an opportunity to see what the alternatives might be. In January, when Petrov and hopefully Delph are both fully fit again there could be some interesting selection dilemmas. Although, given how long he has been out and his inexperience at this level, I reckon we shouldn't count on much from Delph this season. Some appearances from the bench probably.
Perhaps people will begin to appreciate Petrov a bit while he's out of action. In my view he's very under rated however it will be interesting to see Sidwell get a run of games, as he just hasn't had a decent run of games to prove himself for a couple of years. He is however, a scapegoat in waiting and he'll be the first person to blame if anything goes wrong. When we went on our really good run a couple of years ago (away wins at Arse, Everton etc) Sidwell was ever present and on the whole played well. This might just be his opportunity to shine, as he can be a quality player.