Is rubbing alcohol ingestion fatal if an alcoholic drinks it in desperation or accidentally?

Poisoning. Yes, it can be fatal with large amount ingested, and if emergent medical care is delayed. So can alcoholic beverages!
Dangerous. Rubbing alcohol has ethyl alcohol and isopropyl alcohol. Either in large quantities can result in toxicity. Isopropyl alcohol itself affect the central nervous system and can lead to stupor or coma. The effects occur within one to two hours of ingestion. Should ingestion of rubbing alcohol occur, seek medical assistance immediately.