Johann VII killed himself in 1592. But if he kills himself in 1587, it happens before his kids was born and his estate goes to his uncle Ulrich.
Ulrich in OTL had only one daugther who married the king of Denmark, his position as Lutheran Administrator of Schwerin was inherited by his grandson Ulrich of Denmark, while his duchy was inherited by the second son of Johann VII.
So suddenly we have a quite different position at his death, his nearest relative in paternal line is his childless brother Karl I (who dies in 1610), and after that the Mecklenburg dynasty dies out.
This mean we get to the female lines
the nearest heirs is Friedrich Kettler of Courland and Christian IV of Denmark (and his brother Ulrich).
Ulrich and Christian both a better claim than Friedrich Kettler by their grandfather having been brother of Karl I, while Friedrich's mother was Karl's sister.
So likely we see Mecklenburg split between Christian and Ulrich, or we could see Ulrich still only the Bishopric of Schwerin, while Christian become duke of the entire Mecklenburg (not entire unlikely, Ulrich seem to have been a loyal vassal of his brother, after they final dealt with his inherience in Schlewig-Holstein). But even if he get part of Mecklenburg his marriage was morganatic and his possession would return to his brother at his death in 1624.
So we see a Mecklenburg being included in the Oldenburg dynastic possesions from 1610.
So we see Christian IV have a even stronger position in North Germany in the early 17th century.
In fact the Schleswig-Holstein-Mecklenburg combo (with Gottorp, Oldenburg and Bremen-Verden under at the time friendly sidelines) is quite strong, stronger than Brandenburg.