Final answer:
The sentence suggests irony in that setting the boat on fire might lead to rescue, an outcome opposite to the destruction of their safety vessel.
Step-by-step explanation:
The correct summary of the sentence "If we set the boat on fire, there's a chance someone may see us before the boat sinks." is that it is ironic that destroying the boat, which is currently keeping them afloat, may actually be their salvation by signaling for help. There is no mention of sarcasm suggesting not to set the boat on fire, nor is the situation directly related to satire or described as being full of understated despair. Instead, the sentence portrays a situation where the characters are considering a desperate measure to attract attention for rescue, which would paradoxically involve damaging their only means of staying above water. This embodies the literary device of irony, specifically situational irony, where actions have an effect that is opposite from what was intended, so that the outcome is contrary to what was expected.