Teams lose top players all the time, you can either accept that, or ignore it. We've lost Alonso, Mascherano and Torres recently, and a few more. We will lose more players. You can ignore it, let them run down contracts, sell them for nothing, see them decline in form, but it's best to be realistic about these things and try to do the best in the long term for the club. The flip side is that we have replaced all the great players that have left, eventually.
I love having Suarez in the team and I'd love him stay here forever, and I'd love him to stay in this form forever. But neither are likely to happen. If we don't look to plan for what will happen, it won't turn out well.
Obviously it's not a case of selling him for any offer, but if a huge one comes in, we should definitely consider it, and see what players we could get with that money.