Friar John got sent back to Verona because of the quarantine he encountered on the way to Mantua.
Friar Lawrence organises for Friar John to bring Romeo news of Friar Lawrence and Juliets plan (Act Five, Scene 1)
If the messenger in question is Balthazar at the beginning of Act 5, he says she's dead.
The Nurse
The messenger who was supposed to tell him got quarantined and couldn't deliver his message.
His messenger, Friar John, was quarantined.
He's a messenger, the guy who's supposed to tell Romeo that Juliet's death is a fake. But he's not a very good messenger; he fails to get the message to Romeo. (Did he think maybe to tell Romeo's man Balthazar?)
Romeo fails to receive Friar Laurence's message due to the epidemic occurring in the city. Friar Laurence gets quarantined and is unable to bring the letter to Romeo.
Juliet says that if he is serious and plans to marry her, she will send a messenger to meet him at nine o'clock. This messenger will be the Nurse, of course. Romeo will then reveal whatever wedding plans he's made to her. Have you noticed how little wedding planning Juliet does in the play?
The messenger who was supposed to tell him got quarantined and couldn't deliver his message.
the Nurse
Romeo's special messenger.
His messenger, Friar John, was quarantined.
He's a messenger, the guy who's supposed to tell Romeo that Juliet's death is a fake. But he's not a very good messenger; he fails to get the message to Romeo. (Did he think maybe to tell Romeo's man Balthazar?)
The sun!
Romeo fails to receive Friar Laurence's message due to the epidemic occurring in the city. Friar Laurence gets quarantined and is unable to bring the letter to Romeo.
Friar John, who was sent as a messenger to Romeo from Friar Lawrence, was unable to deliver the letter. Because their was some kind of disease issue going on in Mantua that Friar John can't stand it. so, Romeo ended up with no letter receiving and was unable to know that Juliet was faking the death.
Juliet's messenger, Friar Lawrence, is supposed to meet Romeo at 9am to discuss their plan for Juliet to fake her death so she can be with Romeo. They need to ensure that Romeo is aware of the plan and knows what to do next.
Two reasons: first because the messenger Friar John ended up being quarantined so he didn't deliver the message and second because Capulet changed the wedding date so the time when Romeo was supposed to pick up Juliet was 24 hours too late anyway.
Juliet says that if he is serious and plans to marry her, she will send a messenger to meet him at nine o'clock. This messenger will be the Nurse, of course. Romeo will then reveal whatever wedding plans he's made to her. Have you noticed how little wedding planning Juliet does in the play?
Friar John is prevented from delivering his message to Romeo because he is quarantined due to a suspected outbreak of the plague and is unable to leave Verona. This prevents Romeo from receiving vital information about Juliet's plan, leading to tragic consequences.