This language regarding those who opted-out (signed releases) is very strict and therefore, it seems unlikely those people would sue at some point forward. See below.
"Upon the Effective Date, the LTW Holders unconditionally, fully, finally, and forever waive and release the Debtors, each of the Debtors’ chapter 11 estates, the Reorganized Debtors, and their respective past or present parent entities and directors and officers, from any and all claims, demands, rights, liabilities, or causes of action of any and every kind, character or nature whatsoever, in law or in equity, known or unknown, whether asserted or unasserted, which the LTW Holders or anyone claiming through them, on their behalf or for their benefit have or may have or claim to have, now or in the future, against the Debtors, or any of them, that are based upon, related to, or arise out of or in connection with the LTWs, or any claim, act, fact, transaction, occurrence, statement, or omission in connection with, or alleged or that could have been alleged in connection with the LTWs; provided, however, that the LTW Holders may assert any such claims defensively in connection with any action brought against them; and, provided, further, that the LTW Holders shall be entitled to any and all distributions pursuant to the Seventh Amended Plan relating to the Allowed LTW Claims; and, provided, further, that the foregoing release shall not preclude the LTW Holders from participating in any settlement recoveries payable by third parties (other than the claims and causes of action in the Dime Warrants Action being settled hereunder) to equity security holders of WMI."