Tape also has a problem shared with hard disks - to achieve high density we've rapidly hit a stage where the technology is too complex to enable data archeology at some point in the future; using 90s era complexity hard drives is about where the archeological limit is. LTO-1 may even be beyond that complexity compared to DLT, QIC or even Data8 (helical scan may be too much of a spanner in the works)

Modern polymers may make microfiche/microfilm a longer term solution than it has been in the past with acetate film/slides, but I'm not sure how much research has been done into which polymers might be best.

For longer than a century, our best experience is, thus far, with clay and paper (assuming good quality acid-free paper, rather than cheap modern consumer paper).