I've no detailed knowledge of any of the bus operators in Sussex so can't give a definitive answer.
There's little to lose by making contact and asking (with some potential employers, it's hard to get hold of an actual person to talk to, rather than going through the full application process and then finding out something that might have put you off applying in the first place...) These days it's not as if it will even cost you the price of a stamp.
There certainly are PCV licence holders who move between bus driving and other jobs, it's certainly not unusual to go back to bus driving after something else. (it would probably be an advantage if your CPC is up to date but may not be a huge deal if you need the odd day.)
Some operators prefer to take on new trainees rather than existing PCV holders (who in their view may have picked up bad habits elsewhere), others don't do much training and only take on existing PCV holders, and some may be less keen on having trainees working closely with instructors during Covid.
Depending on just where in Sussex you are, there will be some people who have been laid off from jobs (PCV driving or otherwise) at, or related to, Gatwick Airport, and it's hard to say if or when airports will be back to normal. Similarly, most coach operators are largely down to just school contracts at the moment.
Would an approach to one of your former employer be worth making? (not clear if you have moved house since) - some operators have a rule that they won't take people back if they have left in the past, some are quite content to (unless there are specific reasons for that individual), some have a rule (written or otherwise) that you can leave and come back once but not twice. Bear in mind you'd probably end up back on the 'new starter' pay rate (albeit a 'new starter' with PCV licence may go on to a higher rate than a trainee) and be starting again for seniority. Ultimately, the worst they can do is say 'no'.
Quite what the future holds is not certain. Bus services are at present being propped up by the Government's Covid Bus Services Support Grant, which will end eventually. There was a
government announcement last month of new funds for buses in the medium term, although it's not yet clear what proportions of this will go to consultants for feasibility studies on big infrastructure projects, actual infrastructure spending, or revenue support to run more bus journeys.
Some operators have privately made at least outline plans for a 'new normal' that involve fewer buses on the road (it's likely that full week office employment and town centre shopping won't get back to quite the same levels they were before lockdowns) and these will range from lower frequencies to route withdrawals and some depot closures. Some operators are already pursuing cuts to bus drivers' pay and conditions, and a few operators / depots have already closed during Covid.
As 'Andy Pacer' has said, there are chances to move upwards from bus driving - a common first step is a 'relief' role of some sort, driving most of the time and covering an office / supervisor / controller job for holidays / sickness / busy periods. This usually stands you in a good position when there's a vacancy for a similar role full time (the exact roles vary from one company to another.) Although there can be a lot of competition for this, and it's more of a step up in terms of status rather than take-home pay, as a driver who works a fair bit of overtime can take home more than a supervisor who's on a slightly higher hourly rate. And the people who get in to supervisory levels tend to stay in the business, so vacancies can be a case of waiting for someone to retire.
In some of the bigger plc's, there can be something of a divide between the 'supervisor' level roles that drivers can get in to and the 'manager' level roles that go to people from the group's graduate trainee scheme. Some are more progressive than others, Go-Ahead London (for example) offers drivers the chance to get on a 'pre promotion course' and there are people at depot manager level who have come through that path rather than the graduate entry path.
And in some of the smaller companies, the only way in to management is to be - or marry - one of the family that owns it, although there can be occasional opportunities in a small company where the owner doesn't have children (or doesn't have children who want to take the business on.)
