Conclusion
Of course, it's going to be awesome. But it's impossible.
Having two stars like this on the same team won't pan out well in any direction for a club, be it financially or morally.
Buying them will cost a huge amount of money and it may deplete a club's financial resources. Even if they do manage to grab their signature, a lot of money will be shelled out as wages and this will be unsustainable.
The authority that they will exude will reduce the importance and the status of other players of the team and the limelight will be stuck on Messi and Ronaldo only, which will prove to be detrimental to the club. Other players and members will feel unsettled and unsatisfied.
Further, there will definitely be a lot of ego clashes between the duo and it will eventually lead to a lack of chemistry and understanding both on and off the pitch. All completely undesirable.
They may destroy teams for sure, but them in the same team? It'll destroy football instead.
How about we just be grateful to be living in an era when these two legends are playing, eh lads?