I did something similar on my son's bike when the smallest gog on the cheap-a** cassette self destructed on a ride. The small cog broke in pieces and fell on the ground. It went from a free wheel to a no wheel as the remaining cogs fell off their splines. I fixed it by putting a zip tie in the space where the gog was. It held for the 25 miles to get home.

Ride Safe,

Joe