Totally safe to drive with faulty O2 for some time. It'd run rich and that's all.
There's only 1 possible solution for certain: get a new sensor. If you wanna give it a shot, try hard resetting the ECU by removing both battery terminals and touching them together for few secs.
For OBD-2 thingy, search the forum.
API SG Havoline is not recommended in your car. You should stick to API SM/SN.
But using that for short period shouldn't cause the damage anyway.
Swift is notorious for failing on O2 sensors and rear wheel bearings. No biggie IMO.
On a related note, I would never ever recommend using 5w20 oil in pretty much any car in Pakistan. That's not right viscosity for your car and summer temperatures. Better switch to 5w40 ZIC XQ and stretch the drain interval.