What are the structural and health issues for a long-time slow-leaking toilet?
If there is mold on the basement ceiling, it is highly likely that there is mold growing behind the drywall where water has wicked up the bathroom walls -especially if this has been an ongoing, untreated problem. I personally would not try to save money at the risk of leaving mold growing in that area. 

Mold can trigger a host of health problems, some very serious. I once met a woman who had a condition where she was debilitated by sensitivity to perfumes and artificial fragrances (contact or exposure could cause her to be be bed-ridden for months at a time. The weekend I had met her was the first time in three years that she had left her house (her home was a strictly controlled environment - air filters, hermetically sealed rooms, the whole nine yards. She explained that her condition was triggered due to living in a basement for about 8 months where mold was present in the ceiling (she didn't find out about the mold until after she came down with the health problem. I know this is an extreme example, but it is one example of what can happen if mold is left unabated.

Sorry about the verbose response, but take the repairs seriously and don't skimp out just to save time or money. Your long term health is worth the up-front cost of repairs.