No it would not be cut in half since users are investing their dollars by buying Steem Power for example. So the amount of Steem released with each block i.e. the rewardpool stays the same but the value of Steem will probably go up since having so many users makes any social network more valuable assuming they bring valuable knowledge and fun! to the network.

But of course when users flee then the price of Steem in dollars will go down.

Each new block created by the witnesses creates a set amount of new Steem.
The majority of this new Steem created with each block is divided up and paid out to the authors and curators of content on the platform (is it paid out to only the items included in that specific block?)
The amount of new Steem created with each block will decrease over time as the inflation rate decreases.
Based on the above, it seems like there is a set amount of Steem available as rewards, so if for example the number of active users on the platform doubled, then would the rewards be cut in half? Meaning if my upvote is previously worth $1 it would now be worth $0.5? If that is the case then I don't see how the platform can sustain significant growth, which is in theory what we are all hoping for.