Swanson has put up 5.9 fWAR as a Cub.
How to value each fWAR is always in a bit of flux -- subject to the whims of the market, inflation, etc... But $8M per is still a pretty conservative estimate.
So Swanson has been worth something like $47M so far. If he's paid out at $52M by the end of the year, he's roughly "on pace" to provide the value we are supposed to get.
However, given the aging curve, the reality is that "on pace" is behind -- you expect to get more from people early in the contract and little later on. He was on track with that last year, putting up north of 4.5 fWAR and roughly $35M in value.
TL;DR: Swanson was worth way more than his contract last season. He's likely to rack up enough value the rest of this season as to say he hasn't truly disappointed the contract yet. But if he doesn't bounce back to previously established levels next year, the odds of him living up to the contract are low.