It depends on so many factors I think it is almost impossible to guess.

You would need to perform several successful crosses to even get to 25% Autoflower imho - but so many factors....

If the Sativa is an early flowering variety then that could help but that is a real over-simplification. Lowryder crossed F1/F2's are not really that stable as far as I know.

Also you may have issues cloning so even if you get a stable cross you can't easily replicate it or hold the genetics in any way. If it autoflowers you may well not be able to clone at all.

Hope that isn't too dismal - if you want to try it though I say go for it should be a fun smoke Just don't expect to be able to create a "keeper"