If I were to comment strictly based on heart, I would agree with you.
But in reality I don't think it'll be a concern at all.
First of all, we score around 100 goals each of the last two seasons, 100! Of which around 20 came from Kun. Goals come from our entire attack and midfield, with the occasional freak headed corner from our defenders. Just take a look at how many goals we have scored since his latest injury. It's a lot.
And secondly, - we will not try to replace Kun with another Kun, but instead go for someone else who will add to the totality of the squad. Now this someone else needs to be a great player, of course, but might have very different attributes than Aguero. I'm personally not sure of what kind of striker profile we are in need of to be honest, but I suspect it will be an even more all-round striker than Kun, someone more like Jesús, someone who will operate over the entire width of the field if called for, as well as doing a defensive job. Not an easy player profile to find.
But whomever it will be, it will NOT be a Aguero replacement. It will be something and something different. And who knows, - maybe someone who will make us even better?
In Pep and management I trust.
(Discalimer - I love Kun to bits and pieces.)