It seems like Kepa has felt comfortable at the Real Madrid club during this loan period and is reluctant to return to Chelsea. I think this is a good thing for Real Madrid if they want to buy this player while Thibaut Cuortois is injured and will be out for a long time. There is nothing wrong with Real Madrid buy the goalkeeper.
If Thibaut Cuortuos has recovered from injury, I am worried that Thibaut Cuortuos will experience a decline in performance, so I think making Kepa permanent is a good decision and because of his love for Real Madrid, it will have a positive impact on the club and so far Kepa has performed well during his time at Real Madrid.
I suspect he has a personal love for Real Madrid and he is more comfortable in his home country Spain. And he also has the opportunity to play in the Champions League in Madrid. Chelsea is not even sure to play in Europe next season, so Kepa Arrizabalaga took the right option. For the few times he has spent in Real Madrid, his performance has not been disappointing so the club made the right decision if he is offered a permanent deal.
Signing Kepa wouldn't be a bad idea since Courtois hasn't recovered yet from injury, so at this point Kepa is the alternative Real Madrid have for now and considering his goal keeping techniques, I believe since he is doing a great job at Madrid it will be wise to sign him permanently even if Courtois recovers from Injury both of them can be rationing Madrid's goal keeping.
Courtois will also need more time to be fit after his recovery, hence there is a need to sign Kepa permanently. But the issue is whether will Kepa agree to be in the reserve. I am sure that immediately Courtois recovers, he take back the number one spot while Kepa will have to move to the bench. Kepa will only retain his first-team position if Courtois' performance has reduced and maybe he finally retires from active football.