Question: Does Cell Ranger need the I1 FASTQ file to run?
Answer: In most cases, no. If the libraries were made using 5' gene expression, or V(D)J assay, or v2+ chemistry for 3' gene expression, you do not need I1 FASTQ files for running Cell Ranger. This is because the 10x barcode is in R1 FASTQ files.
However, if you are using data from libraries made with 3'v1 chemistry, you will need the I1 files because they contain the 10x barcode. This is most likely to come into play when analyzing published or legacy datasets. Related KB: How to format v1 chemistry datasets to work with current cellranger versions?