I don't think that the suicide rate is affected significantly by private firearm ownership. Canada for example has a comparable, if not a higher, suicide rate than that in the USA even though Canada has much tougher screening for legal firearm owners, very strict storage and transportation laws, and a low rate of firearm ownership in comparison to the USA to begin with.
Of course it could be that living in Canada just makes people much more depressed than those living in the USA, but polls and sociological data offer no evidence for it.
Existing laws (at least in Canada) allow intervention which actually removes the person from their home rather than the firearms, provided a court judge considers the evidence of urgency adequate. But removing someone's property because they're depressed and depressed people sometimes commit suicide would be a violation of rights in my opinion.