The forums have a few stories of this over the years
https://www.mobileread.com/forums/sh...d.php?t=275518
https://www.mobileread.com/forums/sh...d.php?t=225940
https://www.mobileread.com/forums/sh...d.php?t=275518
https://www.mobileread.com/forums/sh...d.php?t=322865
Not all the above are success stories. But all back up that without an external sd card slot the chance of critical failure increases. I’m not sure if a improperly imaged card would mount which would mean you’d have to replace it and image it with the appropriate kobo image.