KevinSchultz gave a very thorough answers and I agrees with him.
To elaborate a bit more.
In general, an unprepared magus may or may not be able to face an unexpected situation. However, given time, a covenant of a few magi can overcome any problem by dedicating enough season of work.
In the case you are describing, the disappearance of Redcap, a few scenarios are possible:
- They are fading slowly away, so magi noticed a decrease in Mercere's service performance. When it starts affecting their work, magi will investigate and either stop the problem and restore the system or implement an alternative solution. All in all, no impact on the learning curve.
- Mercere's services stop suddendly. Immediate investigation from all magi, since we are not only talking about Redcap but also Mercere magi, their domus magnus which is both the Fort Knox of virtus and the central post office with hundreds of very private message in transit and records of agreements, deals and secret history. That's going to be investigate very, very quickly by a lot of very powerful and concerned magi, with a good pinch of Quaesitores thrown in. There will a few years of uncertainty, but quickly ad hoc replacement will be but in place. Since Mercere's mission was a legacy of the first Primi and they earned trust over centuries of faithful and dedication, it will take time to find a substitute. But I would see a subgroup of magi and companion, not unlike the hoplite emerging. Although instead of being know as defender of the Order, they will be know as faithful servant of the Order. They could swear an specific Oath and have certain privileges balanced with obligation. All in all, a rebirth of House Mercere, but instead of being a specific House, more a subgroup of mages from every House dedicated to fulfill some of Mercere's role.
In this case, after a few initial rocky years, business with resume as normal, maybe with some new quirks, maybe with less frequent, but more bulk delivery as mentionned Kevin. So learning will not be affected.
According to your initial question, the disappearance of Redcap's service happen at least a few decades ago. There is plenty of magical tools to replace Mercere's service:
- for urgent delivery, teleporting or flying messenger already exists in RAW.
- for bulk delivery, create flying, invisible boat takes some ressources, but is very doable (exemple of the Sylph, which takes 5 seasons in total to build, with the highest labtotal required of 34 in ReHe to instill the various effects)
- for vis lending, I would see here at least three Houses jumping on the occasion to fill the vacuum: House Tremere knows since a very long time the value of controlling ressources and becoming the virtus bank of the Order would put then in a very strong situation to be able to infer a lot of things just base on virtus transaction (how much and which time of virtus is sought of by such and such is pretty useful info - like tracking now credit card usage), Jerbiton because of their more frequent contact with the mundane world are first hand witness of the Venitian and Lombar banker development and could easily copy-paste their ways of working, and finally House Verditius would love to be in this business to cut the middle man and be in direct control of their most useful ressources. In fact, you can have all three competing and offering services with various benefices and drawbacks.
I only see a couple of things that could be lost for good and hard to replace:
- Mercere's Portal. They are the equivalent of Hermes Portal except that they are permanent. It is a secret kept by the House, so depending how they disappeared, it was kept or lost. Some Bonisagus might be very keen on rediscovery this lost secret.
- Mercere's secret rituals. It is hinted in a few books that's altough there is more efficient ways to deliver message that walking from covenant to covenant, the reason redcaps keep doing it could be some secret road rituals originating from the old Roman road network. Is it true or was it just a rumor spread by redcaps to enhance their role and importance ?
- Then there is also the bloodline of Mutantum magician, which would be a great loss until their abilities are integrated in Magic Theory.