I would replace it all. A new back splash is pretty cheap especially if your doing the work yourself. Just be careful when you pull the old tile off you don't damage the sheet rock.

A pic from further back would help solicite advice but I would probably offer a discount and let the new owner decide, sight unseen.

depends what the granite will be

if it will work with existing backsplash i see no reason to change the backsplash

if it will clash then change by all means

one needs to see the materials and the kitchen to answer properly. it should all work together and make sense within the context of your house

and you should't overdo it for people whose tastes you don't know. neither should you underdo it just because the listing would mention "granite countertops".

Frankly, I never liked this kind of backsplash yet I'd never rip it out upon buying a house if it makes sense with the general color scheme etc, until I decide to remodel for example-which might be years down the road. Neither I'd expect for the house to cost less because it has backsplash that I'm not mad about. If buyers will be bugged by it so much well they'll redo it themselves when they can. Your concern is to make it a cohesive kitchen while preparing it for sale.

Most of the time I recommend talking to a realtor first because too often a new countertop ends up in the landfill because it wasn't what the buyer wanted. A lot depends on the area you are in, though I have to admit, tile countertops are not popular. Do not do the cheapest granite out there - it isn't very pretty either. You might even consider a pretty laminate with a subway tile backsplash. That might make a buyer feel that they had a nice enough kitchen for a few years till they could do what they wanted.

My counter is quartz, but you could do similar with a laminate:

[https://www.houzz.com/photos/my-pics-work-in-progress-phvw-vp~57088087[(https://www.houzz.com/photos/my-pics-work-in-progress-phvw-vp~57088087)

You might end up having to remove the backsplash--counters don't always come out nicely and it might get damaged. So at least be prepared for that possibility.

The backsplash has fancy accent tiles. What does the rest of the kitchen look like? A photo showing a complete wall would be helpful.