I can literally count on one hand the number of members we've had put on the 10 year path at renewal. It's always good to know worst case scenario but it is HIGHLY unlikely you would end up on that route.
I agree with what KFdancer says -
You'll be put on the 10 year path IF you have children together who live in the UK. If you do not have a child together who lives in the UK, you would NOT be put on the 10 year path.
The 10 year route (30 month visa x 4 to ILR) can sometimes go to those with a British child living in the UK, but it is not a given as it is leave outside of the rules. The conditions for that 10 year route, must be met at every 30 month application and as said, the fee and IHS must also be paid with that application.
If your visa to remain is refused, UKVI then look to see if there is another claim for leave outside of the rules. If there is a British child, they will see if the applicant meets the present requirement to start on the 10 year route and if they do, they issue the first of those 30 month visas. If not, they look at any Human Rights claim the applicant might have and if there isn't one, they refuse the HR claim and then send the refusal. Because of all the abuse, in-country appeals have eneded.
It's how some parents end up on the 10 year route when they just wanted FLR(M) and another 30 months to be able to apply for ILR, but they didn't send in everything they were meant to and it caused a refusal of FLR(M).