I am not sure if they will be as good, but they already won a world cup so I do not think that it will matter all that much. They do have a decent number of players but I do not think that they are good enough to win anything anymore, it's not just about Messi or not, you can put a 30 year old Messi into this club and it would still be hard.
It's a marvelous achievement that they won the world cup, it was definitely a great success but I do not see their team talented enough anymore, they just do not look like it to me. Maybe I am mistaken, after all they won the world cup title, so they must be good, but to me the roster itself is not that amazing, look at the roster and valuations to see what I am trying to say here.
I don't want to make a judgement based on the valuation. Anyway, at this point Argentina looks like the strongest team to me (even without Messi). It may be due to the fact that they have very good players and team bonding. Or maybe due to the fact that the other teams are in decline (especially the ones from UEFA confederation). IMO, there are no other team at the same level where Argentina is right now. I would say that Brazil and France are one level below Argentina. Take out Neymar and you will find Brazil unable to compete in a meaningful way against Argentina.