If another county has placed a detainer on your person, the release on the 28th will not be a release into the community. Instead of walking out the front door, he will transfer directly into the custody of the county that filed the detainer.
A detainer is a formal legal hold placed by one jurisdiction requesting that another facility notify them before releasing an individual and hold them briefly so they can take custody. When that detainer is active on the 28th, the releasing facility is legally required to honor it rather than simply letting him go. The maxout date ends his current sentence but the detainer immediately activates and prevents free release.
The missed court date due to snow is a separate but related issue. That court date was likely the proceeding the other county needs him present for, and missing it does not make the detainer go away. It simply means the matter remains unresolved and the other county still has a legal interest in bringing him before their judge.
What happens next after the transfer depends entirely on what the other county's case involves. If it is a warrant for an older matter, he goes before that jurisdiction's judge to answer for it. If bond is set and he can make it, release into the community is still possible. If the matter is serious or if bond is denied, he remains in that county's custody while the case moves forward.
Getting an attorney who can communicate with both jurisdictions simultaneously is the most practical step right now. Understanding exactly what the other county's case involves and what options exist for resolving it quickly is what determines how much additional time this detainer actually costs.