rti - weekly paid

I just had a thought and wondered if anyone knew the answer sorry if it is dumb.

I do a weekly payroll, same person, same amount each week the client pays him cash and I deal with the producing payslip and rti.

As I work by myself what happens if I go away on holiday? Client doesn't know how to use a computer and the software is on my pc.

I know for the first few months there won't be a late fine but thinking long term.