Both have the same operating temperatures, so it's likely that the iPhone 7/7+ would shut down in a similar manner as your 6s+ does.
iPhone 7/7+
Operating ambient temperature: 32° to 95° F (0° to 35° C)
Nonoperating temperature: ‑4° to 113° F (‑20° to 45° C)
Relative humidity: 5% to 95% noncondensing
Operating altitude: tested up to 10,000 feet (3000 m)
iPhone 6s/6s+
Operating ambient temperature: 32° to 95° F (0° to 35° C)
Nonoperating temperature: -4° to 113° F (-20° to 45° C)
Relative humidity: 5% to 95% noncondensing
Operating altitude: tested up to 10,000 feet (3000 m)
iPhone 6s/6s+:
http://www.apple.com/iphone-6s/specs/
iPhone 7/7+:
http://www.apple.com/iphone-7/specs/