Please take the following as only rumors for the time being:
-- In his latest column at Sports Illustrated, Justin Barrasso speculates that Brock Lesnar is expected to drop the WWE Universal title by SummerSlam "at the latest" which seems to imply that it will be at either Extreme Rules in July or SummerSlam itself in August. He adds that because Lesnar is paid by the match, dropping the title could signal that he is leaving the company and headed to the UFC instead.
-- If and when Lesnar leaves WWE, Paul Heyman is expected to be gone as well according to the same article. Apart from being the advocate for Brock Lesnar, WWE reportedly has no further plans for Heyman creatively and with Brock gone, Heyman would effectively become a free agent as well at the end of August.