iMac 5k hard drive failure.

Due lockdown I have not used my iMac regularly for over a year. At most I would boot my Mac up once or twice a month. I have noticed a slowdown In my machine and began to get worried when the last OS update would not install due to drive errors. I have been aware of an issue that would need to be resolved, but not had the time to address it.

Yesterday, I booted the machine up and it froze a couple of minutes into use. On restarting it would not boot and failed to find a OS X partition. I was greeted with a folder with questions mark. Fair to say my drive is gone or not long left. The drive is a SDD and HDD paired. Forgot the name Apple use for it. Sorry.

My question is.

I have no issues with keeping any data on the drive. I have not had time to run proper diagnostics. Sorry. If the HDD is the issue, will it be possible to solely run off the SDD as a boot drive and use an external HDD space to extend the life of the Mac a little longer? I have split the joined-drive before Into Individual drives. Can someone help me through this process please? Terminal? Will the HDD drive failing have an impact on this process?

I know I can replace the failing drive, but I’m not keen on doing this due to spending money on a old model that I won’t be using as my main machine going forward.

Thanks