Update:
My
Tata Play Fiber connection is working fine now since a week. No disconnections at all. Turns out one of their FAT/DP box was faulty and my connection was provisioned from the same DP box. Their technical team identified the issue after I explained everything to one of their senior team member of the area. Thankfully they replaced the whole box and my connection is working fine now.
On the other side, Airtel connection which I got installed 2 weeks ago is down since last 7 days. They just keep sending messages of "unplanned outage" will be resolved by xx:xx time. Can't even raise a SR. I guess I am out of luck here

.
Thankfully Tata folks have resolved my issue and I just paid a month's advance for Airtel connection(they had some offer for Airtel black plans). Will get it disconnected soon as it completely defeats the purpose of a backup broadband connection with such high downtime. I honestly regret opting for their services again and trusting them. I have read some reddit posts and tweets where people are complaining of similar outages(7+days) from
Airtel Xstream Fiber, particularly in my area.
I think it's important for me to have a backup fiber connection given the nature of my work and internet dependency. Other options I have:
1. ACT Fibernet: Pretty new in Pune and went live just a couple of months ago in my colony. They have a lot of ping and routing issues but I have heard good things about it from neighbours, their service response is pretty okay.
2. Gazon Fiber: This is from a LCO and plans are pretty cheap, 500/month for 100 Mbps and 700/month for 200 Mbps. Not a lot of people use it in my colony but a few of them have told me it's good. Pings are great for LCO broadband.
3. Jio Fiber: This is my last option, their response time is pretty bad but uptime is surprisingly good as per neighbours. But ye broadband kam aur cable connection wali feel zyda deta hai

so it's my last option.
4. Microscan Broadband: Nobody uses it in my colony but they do have point of presence here.
Most inclined towards the LCO guy and want to give it a try. 500/month for 100 Mbps seems pretty okay for a backup connection.
My new
Asus router also supports dual Wan aggregation so might set it up in failover mode.