Yeah, 6 months out for Walcott, so obviously misses the World Cup. I actually think it is a very big blow for England, because whilst Townsend would probably have been first choice, England have started to become very reliant on him, and he will be such an obvious target as the attacking outlet. Having Walcott as back up would have allowed him to go flat out for 70 mins and then bring another flying machine on once the weather inevitably takes its toll.
TL;DR England don't have many good attacking options.
As for Arsenal, he has become a more important player and this will test them. Surely they'll go back into the market for a forward now, I think they were planning to anyway.