Not necessarily. As long as Real Madrid and us are still competitive and financially top tier, the two teams will continue to explore and buy new star players. Of course, nobody in the next 100 years or so will replicate the Messi – Ronaldo rivalry and get up to their level.
Barca had R9, Rivaldo, Ronaldinho, but never before Messi-Pep-Cr7, were we and RM considered as Top2.
In 90s, Seria A was by far the most popular and the strongest league.
Until early 00s.
Then EPL came back to life after bans from 80s and 90s.
There weren't a clear best club back then, we had 5-6 big teams who were equally as big (Milan, Juve, Barca, Real, Bayern, Man Utd).
With Messi and Pep, we turned into a No1.
Messi-CR7 rivalry, Cls for Barca, Real, and Uefa Cup for Sevilla turned La Liga into the best league.
Now, without Neymar, CR7 and soon Messi, very likely Barca and RM won't be dominating again, but will turn into one out of top 6-7 clubs again, where clubs will randomly win CLs.
Further, Barca and RM are able to lure mostly SA talents since they love Spanish climate and lifestyle.
But now, after Messi and Neymar, since majority of other Brasilians and Argentinians are meh, what is left? Iscos and Asensios...
EPL is richer and richer and let's see whether RM will be able to steal Kane or similar players.
Coutinho to Barca is understandable.
Neymar to Real could make sense.
Kane to Real, a totally different story.
Look at the list of Ballon D or winners:
https://en.wikipedia.org/wiki/Ballon_d%27Or
2016:
CR7, Messi, Griezmann, top3 from La Liga
2015:
Messi, Cr7, Neymar. All 3 from La liga.
2012:
Messi, Cr7, Iniesta. All 3.
2011:
Messi, Cr7, Xavi.
2010:
Messi, Iniesta, Xavi.
2009:
Messi, Cr7, Xavi.
And then, look at the years BEFORE Messi and Cr7:
2003:
Nedved, Henry, Maldini. Zero from La liga
In other years, La Liga had 1 guy in top3 usually.
This was the only time in a history that two such a great players played in the same time.
And not only that, they played in the same league.
So, Messi-Cr7 level of skills won't be reached soon.
Further, two similar players won't play in La liga again.
Then, we also lost great Xavi and Iniesta.
CL titles will dry out for Barca and Real, who were dominating in the last 12 years with 4+4 titles, all won with Messi and Cr7.
Again, remember that Barca won 1 CL in 100 years before Messi.
Both Barca will have way tougher times after Messi, and a popularity of La liga will take a huge hit AFTER Messi, Cr7, Neymar, Xavi and Iniesta..
For example, La Masia was lucky with 3 guys from this list.
Whom will we have in the future? Roberto, Samper, Alena and Cucu? Hmm...
That doesn't mean that a football will die in Spain, but we need to be objective and accept that this is a huge blow to a popularity of La liga.
Do you CURRENTLY see a new Ballon D Or contender in RM/Barca bar Messi (who won't win it either way)?
In this moment, there are no true Ballon D Or contenders in those two clubs (again, bar Messi).
Maybe if RM will buy Neyclown, La liga will regain a lot of popularity and that would be awesome for us, because RM wouldn't win CLs with that clown, more or less.