That would be sad. Kovacic wants out from RM to play more and then would end up eating the bench of Chelsea.
I mean, I wrote this in higher detail somewhere else a couple days ago but, in short, I was having a hard time thinking of any team Kovacic would go to, one that (I presumed) would be playing Champions League football, and would be able to offer regular starting minutes, or at a minimum high rotational minutes, for Kovacic. And team that I thought would be able to offer that, probably wouldn't be able to pay the asking price that Perez, rightfully so, would be asking for.
Now, a dry loan takes care of that part, and allows Madrid to retain his future rights. Maybe in a year's time the picture will look different in Madrid. I mean, it might look different in a week's time if Modric leaves, something I still doubt personally but whatever, however it appears Mateo is dead set on leaving this season, even if Modric leaves, and even though Zidane is no longer the coach there to sell him on false playing time promises or whatever. It's way too close to the start of the season for Kovacic to start in Chelsea's first game, though, and even the second game could be a pause for question. For his sake, though, I hope he breaks through into Chelsea's starting XI and runs with that spot. We've already seen almost this exact same story play out last year, Madrid selling/loaning a player they (re-)purchased from Serie A, weren't able to give enough playing time to to satisfy them, and then send them off to Chelsea. And that didn't work out terribly well for Morata last season. Hope Mateo has better luck.