Scenario #1: Angels cover the money
John Mozeliak has fleeced teams in the past; see the Nolan Arenado deal for context. It is possible the Cardinals get the Angels to take the large bulk of Trout's contract ($150+ million), and the Cardinals keep key pieces to the lineup. It is unlikely that Perry Minasian will fall for that trap. If the Angels take on a large part of Trout's remaining salary, expect favorite names on the major league roster and key prospects to be sent over to Los Angeles.
If the Angels take the bulk of Trout's contract, leaving the Cardinals with an AAV of $10-$12.5 million over the next 7 years, the Cardinals would have to send quite the conglomeration of talent. We are talking about a package of three of Jordan Walker, Tink Hence, Masyn Winn, and Nolan Gorman PLUS Lars Nootbaar, Brendan Donovan, Dylan Carlson, or Tommy Edman. Also, look for the Cardinals to throw in an A+ player or two for depth to the Angels system.
This trade would severely hurt the team's positional depth and future prospect depth. While the Cardinals would have plenty of money to spend over the next few offseasons, losing at least three current or future starters who have All-Star potential would be painful to swallow. A scenario in which the Angels take on the bulk of Trout's remaining contract would be costly for both teams; therefore, scenario #1 is the least likely to happen.