The friar's desperate plan is a direct result of Juliet's desperation. The friar does prevent Juliet's immediate sui cide and in that way his plan is a success. Of course, we know that his plan will eventually fail because Juliet will kill herself at the end of the play. His plan is intricate and complicated.
Friar Lawrence's plan was Juliet to drink a potion that would put her into a deep sleep, mirroring death. However, Romeo thought she was dead, so he killed himself. AND THEN, Juliet killed herself.
