A failed drug test is one of the most straightforward probation violations there is, and the type of drug involved does not matter. Alcohol can trigger a violation the same way an illegal substance can. The only thing that counts is that a condition of probation was violated, and a positive test is documented proof that it was.
The violation goes back to the original sentencing judge, who has broad discretion in deciding what happens next. The range of outcomes runs from a brief county jail stay of a few weeks at the lenient end all the way to revocation of probation and returning to finish the full original sentence at the other extreme. Where your fiance lands on that spectrum depends on several factors.
His overall compliance history matters. A first violation after an otherwise clean probation record is treated differently from a pattern of violations. The technical violation and the color code failure that preceded the drug test are part of the picture the judge sees, and multiple compliance issues in a short period work against leniency.
The judge's disposition toward the case is the other major variable. Some judges treat a failed drug test as a recoverable situation and respond with a short sanction and modified conditions. Others view it as evidence that the original sentence was too lenient and respond accordingly.
The best outcome requires an attorney making the strongest possible argument before the hearing, presenting context around the positive test, demonstrating any steps your fiance has taken toward addressing substance abuse, and proposing concrete alternatives to incarceration that the judge can consider. Without representation that argument does not get made and the outcome defaults to whatever the court decides on its own.