Transistors can be replaced. If matching transistors are unavailable, often times sets of different transistors can be retrofitted. Though this would probably be a relatively expensive procedure, one would have to consider what the costs would be compared to the much more likely need for frequent tube replacements over a similar time span. Furthermore, the quality of new tube replacements are somewhat suspect, which is evidenced by the ever escalating costs and decreasing availability of of NOS tubes. The likelihood that such a problem will occur with transistors in the realistic need/use of a ss amp is extremely low.
