Restructure means Diggs still gets his money, it's just accounted for differently in the salary cap. One way or another, they have to pay up eventually.
"A typical contract restructure is when a team converts part of a player’s base salary (or a roster bonus) into a signing bonus to create immediate cap relief. This does, however, increase the player’s yearly cap hits thereafter by pushing more dead money into future years."
Complete guide to NFL contract terms, salary structures, and player compensation rules.
operations.nfl.com