Several techie friends say they have gotten their copper left active with a FIOS install by ordering "Data Only FIOS" by phone (not online), and being VERY persistent, both in ordering and at install time. YMMV.

I accidentally got my ex's copper left active because I still had the phone account in my name when she got the FIOS installed in her name, so there was an active phone number on the copper that they didn't have permission to touch.

I let them cut the copper when FIOS was installed in my new townhouse, and in my case they cut it off just below ground level, and didn't dig up the buried copper.

2 reasons to want copper are:
1) Copper stays live during long power outages, because the telco provides the power on it, while POTS over fiber depends on a limited runtime battery backup (unless you provide your own backup to that)
2) Some alarm companies still require copper lines (not normally a technical need, more a headspace problem).

Another reason Verizon wants to switch to fiber is for maintenance - fiber has a fewer and cleaner failure modes than copper, and they can remotely locate many fiber breaks to within inches or at least feet. Fiber mostly either works or doesn't, while copper can degrade multiple ways: increased resistance, bad connections, insulation breaking, crosstalk, water damage, etc.