But with the diadvantages that:
1. You have to mess about changing between train & bus.
2. Due to the inevitable uncertainties about roadworks & congestion, you can never be certain of making connections with onward rail services at the end of the "bus" leg of the journey.
It is fine to arrange relatively straightforward diversions (such as Northampton on the WCML or the Erewash Valley on the Midland Main Line). These often involve waiting around to 'drop back' onto another standard path, to avoid disrupting other services through key nodes. Even then there is often a significant reduction in frequency for some rail journeys, such as Derby-Sheffield or whatever. These kind of diversions are also relatively easy to maintain route knowledge over, often with empty stock moves.
The problem with routes such as Anglo-Scottish is the there is a range of destinations at both the north and south ends - Edinburgh/Glasgow, Euston/Birmingham/Manchester and more. Service alterations and diversions on the core route can quickly spill over into effects at nodes that these days are effectively full. Chronic performance problems in these cities keep many parallel threads going. Even modest numbers of diversions via the Settle & Carlisle or Dumfries can quickly cause problems not only at Manchester, Glasgow and Leeds but also at subsidiary nodes that are far busier and more fragile than they were 25 years ago, such as Blackburn, Shipley and Kilmarnock.
An infrequent alternative service can mean that passengers expecting to make a 'through' journey by rail then discover that they still have to change and hang around for lengthy periods at Preston, Carlisle, Crewe or wherever before travelling on a potentially overcrowded and slow alternative. Meanwhile the users of other services not directly affected by the engineering works can discover that their rolling stock has been cut or taken to resource other routes or their timetable has been slashed to free up paths, quite apart from general performance often taking a hit.
During my career I had many experiences with the operation of amended services on both a pre-planned and emergency basis, organised blockades, procured alternative road transport, supervised arrangements at station level, written publicity material, worked on the development of Schedule 4 and other aspects.
The environment has changed out of all recognition over the years, through motorways, electrification, the move to multiple units, greatly reduced availability of freight locomotives, safety-led restrictions on things like single line working and at last the growing availability of bi-modes. Expecting things to remain the same as they were in the 1980s or whenever is unrealistic.
At least with modern communications, improved station accessibility, low-floor buses and greater availability of things like coffee shops and drinking water at stations the overall passenger experience can often be managed better.