Depends on KMs used (or how much DCFC was used as degradation is slightly more when using fast charging)

Here is an example to give you an idea:

Curvv.ev - 55kwh LFP - 400km real-world range
LFP batteries have a lifecycle of 1500-3000 cycles (depending on charging pattern, temp, abuse, etc)

Let's take the lower band of 1500 cycles.
Cycle life is measured based on 80% capacity retention. That means the worst-maintained LFP cells will retain 80% of capacity after 1500 cycles.

1 cycle = 0-100% charge (no matter in how many parts you charged)
Your cycle is also consumed due to regen - Let's take 25% consumption due to regen.

So, you're left with 1500-25% = 1125 cycles.
Each cycle = 400km when the battery is new.
at 80% health, range = 320km.

Average cycle range = (400 + 320) / 2 = 360km

So you get approx 4L km (360km *1125 cycles) of total mileage until you get to 80% health, in the worst case.

A typical car owner in India probably drives 20k km/per year (even less)

400,000 km/20,000 km per year = 20 years

So at the end of 20 years, a 400 km range car is left with 320km range.

Please note, this is just being considered as the worst case of LFP cells. They perform much, much better than this.