It's "proceeds have". Since the noun "proceeds" only has a plural form, it requires a verb in the plural.
The proceeds have decreased in value.
The proceeds has decreased in value.
Follow the same convention with other verbs to say, for example, "proceeds are" (not "proceeds is") or "proceeds go" (not "proceeds goes").
The proceeds are typically divided among the tenants according to their respective share of the property.
The proceeds is typically divided among the tenants according to their respective share of the property.
And remember, plural nouns take a plural pronoun.
The proceeds from the deal were significant. They went to charity.