Item not received, also- tried many times to contact seller (no reply). Opened case against them (p.pal), can I go & leave neg feedback?

[garienne30]

😞 Even though I have opened a case up through Pay Pal (against the seller);- is it possible to still go and leave feedback for the 'quality' of the transaction? I hope it is okay to do- because I don't want the case to 'finish' (once I escalate it) and 'miss out being able to leave feedback for this transaction' (they were good enough to take my money- but couldn't be bothered to respond even once, to my many attempts to contact them)?
 
Also- does anyone know; if I leave negative feedback (which I have never had to do in all my 8 years on eBay/ until now! but in this instance- I believe it is definitely warranted!);- is there a chance that the seller may get annoyed with me & 'unfairly' leave me 'unwarranted' negative feedback? Over these 8 years I have maintained 100% positive feedback rating~ which I don't want to unfairly loose; if the seller get's annoyed at me, for leaving negative feedback for them? 

 Thanks.