On bond, the odds are low and that is the standard position rather than an exception. When a judge revokes probation and issues a warrant, they are signaling that they do not trust the person to appear voluntarily. Bond exists to ensure appearance at future hearings, and a revocation warrant is already a finding that the conditions of supervision were not met. Most judges hold probation violators without bond until the revocation hearing precisely because the violation itself demonstrates the supervision agreement was not honored.
On getting another chance at probation, the honest estimate is around ten percent, and that number assumes several things going your boyfriend's way simultaneously. A judge who is predisposed toward giving chances, a violation that was technical rather than involving new criminal conduct, genuine remorse demonstrated at the hearing rather than excuses, and a compelling argument from an attorney who knows how to present the case. All of those factors have to align.
What works against him is the fundamental math of revocation. Probation was already the second chance. A revocation hearing is asking for a third chance after the second chance was not completed. Judges who extended leniency and watched it get violated are not generally in a generous frame of mind when that person is back in front of them.
The nature of the violation is the biggest unknown. A technical violation like a missed appointment or a dirty urine is treated differently than a new criminal charge or absconding for months. If the PO's affidavit documenting the violation is detailed and damaging, the case for leniency shrinks considerably.
He needs an attorney before that hearing, not after.